diff --git a/panel/layout/tabs.py b/panel/layout/tabs.py
index ec69035a0e..24076c4679 100644
--- a/panel/layout/tabs.py
+++ b/panel/layout/tabs.py
@@ -151,7 +151,7 @@ def _get_objects(self, model, old_objects, doc, root, comm=None):
                 continue
             elif self.dynamic and i != self.active:
                 child = BkSpacer(**{k: v for k, v in pane.param.get_param_values()
-                                    if k in Layoutable.param})
+                                    if k in Layoutable.param and v is not None})
             else:
                 try:
                     child = pane._get_model(doc, root, model, comm)
diff --git a/panel/models/ace.ts b/panel/models/ace.ts
index 06963a1ca5..84f182bd72 100644
--- a/panel/models/ace.ts
+++ b/panel/models/ace.ts
@@ -135,15 +135,15 @@ export class AcePlot extends HTMLBox {
   static init_AcePlot(): void {
     this.prototype.default_view = AcePlotView
 
-    this.define<AcePlot.Props>({
-      code:         [ p.String            ],
-      filename:     [ p.String            ],
-      language:     [ p.String            ],
-      theme:        [ p.String,  'chrome' ],
-      annotations:  [ p.Array,   []       ],
-      readonly:     [ p.Boolean, false    ],
-      print_margin: [ p.Boolean, false    ]
-    })
+    this.define<AcePlot.Props>(({Any, Array, Boolean, String}) => ({
+      code:         [ String,       '' ],
+      filename:     [ String           ],
+      language:     [ String           ],
+      theme:        [ String, 'chrome' ],
+      annotations:  [ Array(Any),   [] ],
+      readonly:     [ Boolean,   false ],
+      print_margin: [ Boolean,   false ]
+    }))
 
     this.override<AcePlot.Props>({
       height: 300,
diff --git a/panel/models/audio.ts b/panel/models/audio.ts
index f36dd8c22e..937a7e6b30 100644
--- a/panel/models/audio.ts
+++ b/panel/models/audio.ts
@@ -130,13 +130,13 @@ export class Audio extends HTMLBox {
   static init_Audio(): void {
     this.prototype.default_view = AudioView
 
-    this.define<Audio.Props>({
-      loop:     [ p.Boolean,   false ],
-      paused:   [ p.Boolean,   true  ],
-      time:     [ p.Number, 0     ],
-      throttle: [ p.Number, 250   ],
-      value:    [ p.Any,    ''    ],
-      volume:   [ p.Number, null  ],
-    })
+    this.define<Audio.Props>(({Any, Boolean, Int, Number}) => ({
+      loop:     [ Boolean, false ],
+      paused:   [ Boolean,  true ],
+      time:     [ Number,      0 ],
+      throttle: [ Number,    250 ],
+      value:    [ Any,        '' ],
+      volume:   [ Int            ],
+    }))
   }
 }
diff --git a/panel/models/card.ts b/panel/models/card.ts
index e602188dcd..6ecdff9dd5 100644
--- a/panel/models/card.ts
+++ b/panel/models/card.ts
@@ -130,16 +130,16 @@ export class Card extends Column {
   static init_Card(): void {
     this.prototype.default_view = CardView
 
-    this.define<Card.Props>({
-      active_header_background:  [ p.String,  null  ],
-      button_css_classes: [ p.Array,   []    ],
-      collapsed:          [ p.Boolean, true  ],
-      collapsible:        [ p.Boolean, true  ],
-      header_background:  [ p.String,  null  ],
-      header_color:       [ p.String,  null  ],
-      header_css_classes: [ p.Array,   []    ],
-      header_tag:         [ p.String,  "div" ],
-      tag:                [ p.String,  "div" ],
-    })
+    this.define<Card.Props>(({Array, Boolean, Nullable, String}) => ({
+      active_header_background: [ Nullable(String), null ],
+      button_css_classes:       [ Array(String),      [] ],
+      collapsed:                [ Boolean,          true ],
+      collapsible:              [ Boolean,          true ],
+      header_background:        [ Nullable(String), null ],
+      header_color:             [ Nullable(String), null ],
+      header_css_classes:       [ Array(String),      [] ],
+      header_tag:               [ String,          "div" ],
+      tag:                      [ String,          "div" ],
+    }))
   }
 }
diff --git a/panel/models/comm_manager.ts b/panel/models/comm_manager.ts
index cfe88a309f..d58d94f3bb 100644
--- a/panel/models/comm_manager.ts
+++ b/panel/models/comm_manager.ts
@@ -135,12 +135,12 @@ export class CommManager extends Model {
   static init_CommManager(): void {
     this.prototype.default_view = CommManagerView
 
-    this.define<CommManager.Props>({
-      plot_id: [ p.String, null ],
-      comm_id: [ p.String, null ],
-      client_comm_id: [ p.String, null],
-      timeout: [ p.Number, 5000 ],
-      debounce: [ p.Number, 50],
-    })
+    this.define<CommManager.Props>(({Int, String}) => ({
+      plot_id:        [ String    ],
+      comm_id:        [ String    ],
+      client_comm_id: [ String    ],
+      timeout:        [ Int, 5000 ],
+      debounce:       [ Int,   50 ],
+    }))
   }
 }
diff --git a/panel/models/deckgl.ts b/panel/models/deckgl.ts
index 3db09dc0a7..028a2d93b8 100644
--- a/panel/models/deckgl.ts
+++ b/panel/models/deckgl.ts
@@ -1,6 +1,7 @@
 import {div} from "@bokehjs/core/dom"
 import * as p from "@bokehjs/core/properties"
 import {HTMLBox} from "@bokehjs/models/layouts/html_box"
+import {ColumnDataSource} from "@bokehjs/models/sources/column_data_source"
 
 import {transform_cds_to_records} from "./data"
 import {PanelHTMLBoxView, set_size} from "./layout"
@@ -190,7 +191,7 @@ export namespace DeckGLPlot {
   export type Attrs = p.AttrsOf<Props>
   export type Props = HTMLBox.Props & {
     data: p.Property<any>
-    data_sources: p.Property<any[]>
+    data_sources: p.Property<ColumnDataSource[]>
     initialViewState: p.Property<any>
     layers: p.Property<any[]>
     mapbox_api_key: p.Property<string>
@@ -215,17 +216,17 @@ export class DeckGLPlot extends HTMLBox {
   static init_DeckGLPlot(): void {
     this.prototype.default_view = DeckGLPlotView;      
 
-    this.define<DeckGLPlot.Props>({
-      data: [p.Any],
-      data_sources: [ p.Array, [] ],
-      clickState: [ p.Any ],
-      hoverState: [ p.Any ],
-      initialViewState: [p.Any],
-      layers: [ p.Array, [] ],
-      mapbox_api_key: [p.String],
-      tooltip: [ p.Any ],
-      viewState: [ p.Any ],
-    })
+    this.define<DeckGLPlot.Props>(({Any, Array, String, Ref}) => ({
+      data:             [ Any                              ],
+      data_sources:     [ Array(Ref(ColumnDataSource)), [] ],
+      clickState:       [ Any,                          {} ],
+      hoverState:       [ Any,                          {} ],
+      initialViewState: [ Any,                          {} ],
+      layers:           [ Array(Any),                   [] ],
+      mapbox_api_key:   [ String,                       '' ],
+      tooltip:          [ Any,                          {} ],
+      viewState:        [ Any,                          {} ],
+    }))
 
     this.override<DeckGLPlot.Props>({
       height: 400,
diff --git a/panel/models/echarts.ts b/panel/models/echarts.ts
index d62ab22602..ae80708634 100644
--- a/panel/models/echarts.ts
+++ b/panel/models/echarts.ts
@@ -61,10 +61,10 @@ export class ECharts extends HTMLBox {
   static init_ECharts(): void {
     this.prototype.default_view = EChartsView
 
-    this.define<ECharts.Props>({
-      data:  [ p.Any               ],
-      theme: [ p.String, "default" ],
-      renderer: [ p.String, "canvas"]
-    })
+    this.define<ECharts.Props>(({Any, String}) => ({
+      data:     [ Any,           {} ],
+      theme:    [ String, "default" ],
+      renderer: [ String,  "canvas" ]
+    }))
   }
 }
diff --git a/panel/models/file_download.ts b/panel/models/file_download.ts
index fdaedb820e..fc1edc1ed0 100644
--- a/panel/models/file_download.ts
+++ b/panel/models/file_download.ts
@@ -217,15 +217,15 @@ export class FileDownload extends InputWidget {
   static init_FileDownload(): void {
     this.prototype.default_view = FileDownloadView
 
-    this.define<FileDownload.Props>({
-      auto:         [ p.Boolean,        false ],
-      clicks:       [ p.Number,         0     ],
-      data:         [ p.NullString,     null  ],
-      label:        [ p.String,   "Download"  ],
-      filename:     [ p.String,         null  ],
-      button_type:  [ p.ButtonType, "default" ], // TODO (bev)
-      _transfers:   [ p.Number,          0    ],
-    })
+    this.define<FileDownload.Props>(({Boolean, Int, Nullable, String}) => ({
+      auto:         [ Boolean,          false ],
+      clicks:       [ Int,                  0 ],
+      data:         [ Nullable(String),  null ],
+      label:        [ String,      "Download" ],
+      filename:     [ Nullable(String),  null ],
+      button_type:  [ ButtonType,   "default" ], // TODO (bev)
+      _transfers:   [ Int,                  0 ],
+    }))
 
     this.override<FileDownload.Props>({
       title: "",
diff --git a/panel/models/ipywidget.ts b/panel/models/ipywidget.ts
index 01de9bb387..8e65cdc24f 100644
--- a/panel/models/ipywidget.ts
+++ b/panel/models/ipywidget.ts
@@ -74,8 +74,8 @@ export class IPyWidget extends HTMLBox {
   static init_IPyWidget(): void {
     this.prototype.default_view = IPyWidgetView
 
-    this.define<IPyWidget.Props>({
-      bundle: [ p.Any, {} ],
-    })
+    this.define<IPyWidget.Props>(({Any}) => ({
+      bundle: [ Any, {} ],
+    }))
   }
 }
diff --git a/panel/models/json.ts b/panel/models/json.ts
index 3d00c0179a..8e4ac077f1 100644
--- a/panel/models/json.ts
+++ b/panel/models/json.ts
@@ -1,3 +1,4 @@
+import {Enum} from "@bokehjs/core/kinds"
 import * as p from "@bokehjs/core/properties"
 import {Markup} from "@bokehjs/models/widgets/markup"
 import JSONFormatter from "json-formatter-js"
@@ -35,15 +36,14 @@ export class JSONView extends PanelMarkupView {
   }
 }
 
-type Theme = "light" | "dark"
-const Theme: Theme[] = ["dark", "light"]
+export const JSONTheme = Enum("dark", "light")
 
 export namespace JSON {
   export type Attrs = p.AttrsOf<Props>
   export type Props = Markup.Props & {
-    depth: p.Property<number>
+    depth: p.Property<number | null>
     hover_preview: p.Property<boolean> 
-    theme: p.Property<"light" | "dark">
+    theme: p.Property<typeof JSONTheme["__type__"]>
   }
 }
 
@@ -60,10 +60,10 @@ export class JSON extends Markup {
 
   static init_JSON(): void {
     this.prototype.default_view = JSONView
-    this.define<JSON.Props>({
-      depth: [p.Number, 1],
-      hover_preview: [p.Boolean, false],
-      theme: [p.Enum(Theme), "dark"],
-    })
+    this.define<JSON.Props>(({Boolean, Int, Nullable}) => ({
+      depth:         [ Nullable(Int),  1 ],
+      hover_preview: [ Boolean,    false ],
+      theme:         [ JSONTheme, "dark" ],
+    }))
   }
 }
diff --git a/panel/models/layout.py b/panel/models/layout.py
index 7ec2d0bc1f..362a8567b6 100644
--- a/panel/models/layout.py
+++ b/panel/models/layout.py
@@ -1,10 +1,10 @@
-from bokeh.core.properties import String, List, Bool
+from bokeh.core.properties import Bool, List, Nullable, String
 
 from bokeh.models import Column
 
 class Card(Column):
 
-    active_header_background = String(help="Background color of active Card header.")
+    active_header_background = Nullable(String, help="Background color of active Card header.")
 
     button_css_classes = List(String, help="CSS classes to add to the Card collapse button.")
 
@@ -12,9 +12,9 @@ class Card(Column):
 
     collapsible = Bool(True, help="Whether the Card should have a button to collapse it.")
 
-    header_background = String(help="Background color of the Card header.")
+    header_background = Nullable(String, help="Background color of the Card header.")
 
-    header_color = String(help="Color of the header text and butotn.")
+    header_color = Nullable(String, help="Color of the header text and button.")
 
     header_css_classes = List(String, help="CSS classes to add to the Card header.")
 
diff --git a/panel/models/location.ts b/panel/models/location.ts
index d18445ea0d..d414aab13d 100644
--- a/panel/models/location.ts
+++ b/panel/models/location.ts
@@ -77,15 +77,15 @@ export class Location extends Model {
   static init_Location(): void {
     this.prototype.default_view = LocationView;
 
-    this.define<Location.Props>({
-      href: [p.String, ''],
-      hostname: [p.String, ''],
-      pathname: [p.String, ''],
-      protocol: [p.String, ''],
-      port: [p.String, ''],
-      search: [p.String, ''],
-      hash: [p.String, ''],
-      reload: [p.Boolean, false],
-    })
+    this.define<Location.Props>(({Boolean, String}) => ({
+      href:     [ String,     "" ],
+      hostname: [ String,     "" ],
+      pathname: [ String,     "" ],
+      protocol: [ String,     "" ],
+      port:     [ String,     "" ],
+      search:   [ String,     "" ],
+      hash:     [ String,     "" ],
+      reload:   [ Boolean, false ],
+    }))
   }
 }
diff --git a/panel/models/markup.py b/panel/models/markup.py
index d75ebbd518..0b916f66e9 100644
--- a/panel/models/markup.py
+++ b/panel/models/markup.py
@@ -3,7 +3,7 @@
 """
 from __future__ import absolute_import, division, unicode_literals
 
-from bokeh.core.properties import Bool, Either, Int, Float, String
+from bokeh.core.properties import Bool, Either, Int, Float, Nullable, String
 from bokeh.models.widgets import Markup
 
 
@@ -18,7 +18,7 @@ class JSON(Markup):
     A bokeh model that renders JSON as tree.
     """
 
-    depth = Either(Int, Float, default=1, help="Depth to which the JSON tree is expanded.")
+    depth = Either(Nullable(Int), Float, default=1, help="Depth to which the JSON tree is expanded.")
 
     hover_preview = Bool(default=False, help="Whether to show a hover preview for collapsed nodes.")
 
diff --git a/panel/models/player.ts b/panel/models/player.ts
index 7e73ce690e..e5737ec91f 100644
--- a/panel/models/player.ts
+++ b/panel/models/player.ts
@@ -1,3 +1,4 @@
+import {Enum} from "@bokehjs/core/kinds"
 import * as p from "@bokehjs/core/properties"
 import {div} from "@bokehjs/core/dom"
 import {Widget, WidgetView} from "@bokehjs/models/widgets/widget"
@@ -182,8 +183,6 @@ export class PlayerView extends WidgetView {
     this.loop_state.appendChild(reflect)
     this.loop_state.appendChild(reflect_label)
 
-
-
     this.groupEl.appendChild(this.sliderEl)
     this.groupEl.appendChild(button_div)
     if (this.model.show_loop_controls)
@@ -309,6 +308,8 @@ export class PlayerView extends WidgetView {
   }
 }
 
+export const LoopPolicy = Enum("once", "loop", "reflect")
+
 export namespace Player {
   export type Attrs = p.AttrsOf<Props>
   export type Props = Widget.Props & {
@@ -317,12 +318,13 @@ export namespace Player {
     start: p.Property<number>
     end: p.Property<number>
     step: p.Property<number>
-    loop_policy: p.Property<any>
+    loop_policy: p.Property<typeof LoopPolicy["__type__"]>
     value: p.Property<any>
     show_loop_controls: p.Property<boolean>
   }
 }
 
+
 export interface Player extends Player.Attrs {}
 
 export class Player extends Widget {
@@ -338,16 +340,16 @@ export class Player extends Widget {
   static init_Player(): void {
     this.prototype.default_view = PlayerView
 
-    this.define<Player.Props>({
-      direction:          [ p.Number,      0            ],
-      interval:           [ p.Number,      500          ],
-      start:              [ p.Number,                   ],
-      end:                [ p.Number,                   ],
-      step:               [ p.Number,      1            ],
-      loop_policy:        [ p.Any,         "once"       ],
-      value:              [ p.Any,         0            ],
-      show_loop_controls: [ p.Boolean,     true         ],
-    })
+    this.define<Player.Props>(({Boolean, Int}) => ({
+      direction:          [ Int,             0 ],
+      interval:           [ Int,           500 ],
+      start:              [ Int                ],
+      end:                [ Int                ],
+      step:               [ Int,             1 ],
+      loop_policy:        [ LoopPolicy, "once" ],
+      value:              [ Int,             0 ],
+      show_loop_controls: [ Boolean,      true ],
+    }))
 
     this.override<Player.Props>({width: 400})
   }
diff --git a/panel/models/singleselect.ts b/panel/models/singleselect.ts
index 8513c7f2f4..ba97ae655b 100644
--- a/panel/models/singleselect.ts
+++ b/panel/models/singleselect.ts
@@ -106,10 +106,10 @@ export class SingleSelect extends InputWidget {
   static init_SingleSelect(): void {
     this.prototype.default_view = SingleSelectView
 
-    this.define<SingleSelect.Props>({
-      value:   [ p.String, "" ],
-      options: [ p.Array, [] ],
-      size:    [ p.Number, 4 ], // 4 is the HTML default
-    })
+    this.define<SingleSelect.Props>(({Any, Array, Int, String}) => ({
+      value:   [ String,     "" ],
+      options: [ Array(Any), [] ],
+      size:    [ Int,         4 ], // 4 is the HTML default
+    }))
   }
 }
diff --git a/panel/models/state.ts b/panel/models/state.ts
index fd80707e4f..afca65194c 100644
--- a/panel/models/state.ts
+++ b/panel/models/state.ts
@@ -94,11 +94,11 @@ export class State extends Model {
   static init_State(): void {
     this.prototype.default_view = StateView
 
-    this.define<State.Props>({
-      json:    [ p.Boolean, false ],
-      state:   [ p.Any, {}        ],
-      widgets: [ p.Any, {}        ],
-      values:  [ p.Any, []        ],
-    })
+    this.define<State.Props>(({Any, Boolean}) => ({
+      json:    [ Boolean, false ],
+      state:   [ Any,        {} ],
+      widgets: [ Any,        {} ],
+      values:  [ Any,        [] ],
+    }))
   }
 }
diff --git a/panel/models/tabulator.py b/panel/models/tabulator.py
index 7ba1772e98..3381dad648 100644
--- a/panel/models/tabulator.py
+++ b/panel/models/tabulator.py
@@ -4,7 +4,7 @@
 See http://tabulator.info/
 """
 from bokeh.core.properties import (
-    Any, Bool, Dict, Enum, Instance, Int, List, String
+    Any, Bool, Dict, Enum, Instance, Int, List, Nullable, String
 )
 from bokeh.models import ColumnDataSource
 from bokeh.models.layouts import HTMLBox
@@ -37,7 +37,7 @@ class DataTabulator(HTMLBox):
 
     filename = String(default="table.csv")
 
-    follow = Bool()
+    follow = Bool(True)
 
     frozen_rows = List(Int)
 
@@ -51,9 +51,9 @@ class DataTabulator(HTMLBox):
 
     styles = Dict(Int, Dict(Int, List(String)))
 
-    pagination = String()
+    pagination = Nullable(String)
 
-    page = Int()
+    page = Nullable(Int)
 
     page_size = Int()
 
diff --git a/panel/models/tabulator.ts b/panel/models/tabulator.ts
index 04ae34b536..851dffdff8 100644
--- a/panel/models/tabulator.ts
+++ b/panel/models/tabulator.ts
@@ -1,5 +1,6 @@
 import {HTMLBox} from "@bokehjs/models/layouts/html_box"
 import {div} from "@bokehjs/core/dom"
+import {Enum} from "@bokehjs/core/kinds"
 import * as p from "@bokehjs/core/properties";
 import {ColumnDataSource} from "@bokehjs/models/sources/column_data_source";
 import {TableColumn} from "@bokehjs/models/widgets/tables"
@@ -485,9 +486,10 @@ export class DataTabulatorView extends PanelHTMLBoxView {
     this.model.source.patch({[field]: [[index, value]]});
     this._tabulator_cell_updating = false
   }
-
 }
 
+export const TableLayout = Enum("fit_data", "fit_data_fill", "fit_data_stretch", "fit_data_table", "fit_columns")
+
 export namespace DataTabulator {
   export type Attrs = p.AttrsOf<Props>
   export type Props = HTMLBox.Props & {
@@ -500,7 +502,7 @@ export namespace DataTabulator {
     frozen_rows: p.Property<number[]>
     groupby: p.Property<string[]>
     hidden_columns: p.Property<string[]>
-    layout: p.Property<"fit_data" | "fit_data_fill" | "fit_data_stretch" | "fit_data_table" | "fit_columns">
+    layout: p.Property<typeof TableLayout["__type__"]>
     max_page: p.Property<number>
     page: p.Property<number>
     page_size: p.Property<number>
@@ -528,26 +530,26 @@ export class DataTabulator extends HTMLBox {
   static init_DataTabulator(): void {
     this.prototype.default_view = DataTabulatorView;
 
-    this.define<DataTabulator.Props>({
-      configuration: [p.Any, ],
-      columns: [ p.Array, [] ],
-      download: [ p.Boolean, true ],
-      editable: [ p.Boolean, true ],
-      filename: [ p.String, 'table.csv'],
-      follow: [p.Boolean, ],
-      frozen_rows: [ p.Array, []],
-      groupby: [ p.Array, [] ],
-      hidden_columns: [ p.Array, [] ],
-      layout: [ p.Any, "fit_data" ],
-      max_page: [ p.Number, 0 ],
-      pagination: [ p.String, null ],
-      page: [ p.Number, 0],
-      page_size: [ p.Number, 0],
-      source: [ p.Any, ],
-      sorters: [ p.Array, []],
-      styles: [ p.Any, ],
-      theme: [ p.String, "simple"],
-      theme_url: [p.String, "https://unpkg.com/tabulator-tables@4.9.3/dist/css/"]
-    })
+    this.define<DataTabulator.Props>(({Any, Array, Boolean, Nullable, Number, Ref, String}) => ({
+      configuration:  [ Any,                     {} ],
+      columns:        [ Array(Ref(TableColumn)), [] ],
+      download:       [ Boolean,               true ],
+      editable:       [ Boolean,               true ],
+      filename:       [ String,         "table.csv" ],
+      follow:         [ Boolean,               true ],
+      frozen_rows:    [ Array(Number),           [] ],
+      groupby:        [ Array(String),           [] ],
+      hidden_columns: [ Array(String),           [] ],
+      layout:         [ TableLayout,     "fit_data" ],
+      max_page:       [ Number,                   0 ],
+      pagination:     [ Nullable(String),      null ],
+      page:           [ Number,                   0 ],
+      page_size:      [ Number,                   0 ],
+      source:         [ Ref(ColumnDataSource)       ],
+      sorters:        [ Array(Any),              [] ],
+      styles:         [ Any,                     {} ],
+      theme:          [ String,            "simple" ],
+      theme_url:      [ String, "https://unpkg.com/tabulator-tables@4.9.3/dist/css/"]
+    }))
   }
 }
diff --git a/panel/models/vega.py b/panel/models/vega.py
index 8897a985c8..2573fea54c 100644
--- a/panel/models/vega.py
+++ b/panel/models/vega.py
@@ -1,7 +1,7 @@
 """
 Defines custom VegaPlot bokeh model to render Vega json plots.
 """
-from bokeh.core.properties import Dict, String, Any, Instance
+from bokeh.core.properties import Any, Dict, Instance, Nullable, String
 from bokeh.models import LayoutDOM, ColumnDataSource
 
 from ..util import classproperty, bundled_files
@@ -41,6 +41,6 @@ def __js_skip__(cls):
         'exports': {'vega-embed': 'vegaEmbed', 'vega': 'vega', 'vega-lite': 'vl'}
     }
 
-    data = Dict(String, Any)
+    data = Nullable(Dict(String, Any))
 
     data_sources = Dict(String, Instance(ColumnDataSource))
diff --git a/panel/models/vega.ts b/panel/models/vega.ts
index 2a01677134..f975c55415 100644
--- a/panel/models/vega.ts
+++ b/panel/models/vega.ts
@@ -94,9 +94,9 @@ export class VegaPlot extends HTMLBox {
   static init_VegaPlot(): void {
     this.prototype.default_view = VegaPlotView
 
-    this.define<VegaPlot.Props>({
-      data: [ p.Any         ],
-      data_sources: [ p.Any  ],
-    })
+    this.define<VegaPlot.Props>(({Any}) => ({
+      data:         [ Any, {} ],
+      data_sources: [ Any, {} ],
+    }))
   }
 }
diff --git a/panel/models/video.ts b/panel/models/video.ts
index fdeabde529..65c6eb11af 100644
--- a/panel/models/video.ts
+++ b/panel/models/video.ts
@@ -138,13 +138,13 @@ export class Video extends HTMLBox {
   static init_Video(): void {
     this.prototype.default_view = VideoView
 
-    this.define<Video.Props>({
-      loop:     [ p.Boolean,   false ],
-      paused:   [ p.Boolean,   true  ],
-      time:     [ p.Number, 0     ],
-      throttle: [ p.Number, 250   ],
-      value:    [ p.Any,    ''    ],
-      volume:   [ p.Number, null  ],
-    })
+    this.define<Video.Props>(({Any, Boolean, Int, Number}) => ({
+      loop:     [ Boolean, false ],
+      paused:   [ Boolean,  true ],
+      time:     [ Number,      0 ],
+      throttle: [ Int,       250 ],
+      value:    [ Any,        '' ],
+      volume:   [ Int            ],
+    }))
   }
 }
diff --git a/panel/models/videostream.ts b/panel/models/videostream.ts
index a98c4ed427..8f1ae55067 100644
--- a/panel/models/videostream.ts
+++ b/panel/models/videostream.ts
@@ -117,13 +117,13 @@ export class VideoStream extends HTMLBox {
   static init_VideoStream(): void {
     this.prototype.default_view = VideoStreamView
 
-    this.define<VideoStream.Props>({
-      format:   [ p.String, 'png'  ],
-      paused:   [ p.Boolean, false ],
-      snapshot: [ p.Boolean, false ],
-      timeout:  [ p.Number,  0     ],
-      value:    [ p.Any,           ]
-    })
+    this.define<VideoStream.Props>(({Any, Boolean, Number, String}) => ({
+      format:   [ String,  'png' ],
+      paused:   [ Boolean, false ],
+      snapshot: [ Boolean, false ],
+      timeout:  [ Number,      0 ],
+      value:    [ Any            ]
+    }))
 
     this.override<VideoStream.Props>({
       height: 240,
diff --git a/panel/models/vtk.py b/panel/models/vtk.py
index f00fb9d1da..fe7015b282 100644
--- a/panel/models/vtk.py
+++ b/panel/models/vtk.py
@@ -2,9 +2,10 @@
 """
 Defines custom VTKPlot bokeh model to render VTK objects.
 """
-from bokeh.core.properties import (String, Bool, Dict, Any, Override,
-                                   Instance, Int, Float, PositiveInt,
-                                   Enum, List)
+from bokeh.core.properties import (
+    String, Bool, Dict, Any, Override, Instance, Int, Float, PositiveInt,
+    Enum, List, Nullable
+)
 from bokeh.core.has_props import abstract
 from bokeh.core.enums import enumeration
 from bokeh.models import HTMLBox, Model, ColorMapper
@@ -100,7 +101,7 @@ class VTKJSPlot(AbstractVTKPlot):
     Bokeh model for plotting a 3D scene saved in the `.vtk-js` format
     """
 
-    data = String(help="""The serialized vtk.js data""")
+    data = Nullable(String, help="""The serialized vtk.js data""")
 
     enable_keybindings = Bool(default=False)
 
@@ -117,7 +118,7 @@ class VTKVolumePlot(AbstractVTKPlot):
     controller_expanded = Bool(default=True, help="""
         If True the volume controller panel options is expanded in the view""")
 
-    data = Dict(String, Any)
+    data = Nullable(Dict(String, Any))
 
     diffuse = Float(default=0.7)
 
diff --git a/panel/models/vtk/util.ts b/panel/models/vtk/util.ts
index f918f30484..2926f5b577 100644
--- a/panel/models/vtk/util.ts
+++ b/panel/models/vtk/util.ts
@@ -1,4 +1,5 @@
 import {linspace} from "@bokehjs/core/util/array"
+import {Enum} from "@bokehjs/core/kinds"
 
 export const ARRAY_TYPES = {
   uint8:   Uint8Array,
@@ -95,11 +96,16 @@ declare type RGBnode = {
   b: number
 }
 
-export declare type ColorMapper = {
+export type ColorMapper = {
   palette: string[]
   low: number
   high: number
 }
+
+
+export const Interpolation = Enum("fast_linear", "linear", "nearest")
+export type Interpolation = typeof Interpolation["__type__"]
+
 export declare type CSSProperties = {[key: string]: string}
 
 export declare type VolumeType = {
diff --git a/panel/models/vtk/vtkjs.ts b/panel/models/vtk/vtkjs.ts
index d2088b8e63..e7d0f13465 100644
--- a/panel/models/vtk/vtkjs.ts
+++ b/panel/models/vtk/vtkjs.ts
@@ -72,9 +72,9 @@ export class VTKJSPlot extends AbstractVTKPlot {
   static init_VTKJSPlot(): void {
     this.prototype.default_view = VTKJSPlotView
 
-    this.define<VTKJSPlot.Props>({
-      data:               [ p.String         ],
-      enable_keybindings: [ p.Boolean, false ],
-    })
+    this.define<VTKJSPlot.Props>(({Boolean, Nullable, String}) => ({
+      data:               [ Nullable(String)  ],
+      enable_keybindings: [ Boolean, false    ],
+    }))
   }
 }
diff --git a/panel/models/vtk/vtklayout.ts b/panel/models/vtk/vtklayout.ts
index 13876f3edc..dd9df5a269 100644
--- a/panel/models/vtk/vtklayout.ts
+++ b/panel/models/vtk/vtklayout.ts
@@ -381,7 +381,7 @@ export namespace AbstractVTKPlot {
   export type Props = HTMLBox.Props & {
     axes: p.Property<VTKAxes>
     camera: p.Property<any>
-    data: p.Property<string | VolumeType>
+    data: p.Property<string | VolumeType | null>
     enable_keybindings: p.Property<boolean>
     orientation_widget: p.Property<boolean>
     color_mappers: p.Property<ColorMapper[]>
diff --git a/panel/models/vtk/vtkvolume.ts b/panel/models/vtk/vtkvolume.ts
index f7846e60b2..9a37abcaf0 100644
--- a/panel/models/vtk/vtkvolume.ts
+++ b/panel/models/vtk/vtkvolume.ts
@@ -2,15 +2,16 @@ import * as p from "@bokehjs/core/properties"
 
 import {AbstractVTKPlot, AbstractVTKView} from "./vtklayout"
 import {
+  ColorMapper,
+  Interpolation,
   VolumeType,
   vtkns,
   data2VTKImageData,
   hexToRGB,
   vtkLutToMapper,
-  ColorMapper,
 } from "./util"
 
-declare type InterpolationType = "fast_linear" | "linear" | "nearest"
+
 export class VTKVolumePlotView extends AbstractVTKView {
   model: VTKVolumePlot
   protected _controllerWidget: any
@@ -344,7 +345,7 @@ export class VTKVolumePlotView extends AbstractVTKView {
     this._vtk_renwin.getRenderer().addVolume(actor)
   }
 
-  _set_interpolation(interpolation: InterpolationType): void {
+  _set_interpolation(interpolation: Interpolation): void {
     if (interpolation == "fast_linear") {
       this.volume.getProperty().setInterpolationTypeToFastLinear()
       this.image_actor_i.getProperty().setInterpolationTypeToLinear()
@@ -379,7 +380,7 @@ export namespace VTKVolumePlot {
     display_slices: p.Property<boolean>
     display_volume: p.Property<boolean>
     edge_gradient: p.Property<number>
-    interpolation: p.Property<InterpolationType>
+    interpolation: p.Property<Interpolation>
     mapper: p.Property<ColorMapper>
     render_background: p.Property<string>
     rescale: p.Property<boolean>
@@ -406,26 +407,26 @@ export class VTKVolumePlot extends AbstractVTKPlot {
   static init_VTKVolumePlot(): void {
     this.prototype.default_view = VTKVolumePlotView
 
-    this.define<VTKVolumePlot.Props>({
-      ambient:              [ p.Number,            0.2 ],
-      colormap:             [ p.String                 ],
-      data:                 [ p.Instance               ],
-      diffuse:              [ p.Number,            0.7 ],
-      display_slices:       [ p.Boolean,         false ],
-      display_volume:       [ p.Boolean,          true ],
-      edge_gradient:        [ p.Number,            0.2 ],
-      interpolation:        [ p.Any,      'fast_linear'],
-      mapper:               [ p.Instance               ],
-      render_background:    [ p.String,      '#52576e' ],
-      rescale:              [ p.Boolean,         false ],
-      sampling:             [ p.Number,            0.4 ],
-      shadow:               [ p.Boolean,          true ],
-      slice_i:              [ p.Int,               0   ],
-      slice_j:              [ p.Int,               0   ],
-      slice_k:              [ p.Int,               0   ],
-      specular:             [ p.Number,            0.3 ],
-      specular_power:       [ p.Number,            8.0 ],
-      controller_expanded:  [ p.Boolean,          true ],
-    })
+    this.define<VTKVolumePlot.Props>(({Any, Array, Boolean, Int, Number, String, Struct}) => ({
+      ambient:              [ Number,            0.2 ],
+      colormap:             [ String                 ],
+      data:                 [ Any                    ],
+      diffuse:              [ Number,            0.7 ],
+      display_slices:       [ Boolean,         false ],
+      display_volume:       [ Boolean,          true ],
+      edge_gradient:        [ Number,            0.2 ],
+      interpolation:        [ Interpolation, 'fast_linear'],
+      mapper:               [ Struct({palette: Array(String), low: Number, high: Number}) ],
+      render_background:    [ String,      '#52576e' ],
+      rescale:              [ Boolean,         false ],
+      sampling:             [ Number,            0.4 ],
+      shadow:               [ Boolean,          true ],
+      slice_i:              [ Int,               0   ],
+      slice_j:              [ Int,               0   ],
+      slice_k:              [ Int,               0   ],
+      specular:             [ Number,            0.3 ],
+      specular_power:       [ Number,            8.0 ],
+      controller_expanded:  [ Boolean,          true ],
+    }))
   }
 }
diff --git a/panel/models/widgets.py b/panel/models/widgets.py
index 945fb49b52..4fbcc429f5 100644
--- a/panel/models/widgets.py
+++ b/panel/models/widgets.py
@@ -93,7 +93,7 @@ class Video(HTMLBox):
 
     value = Any(help="Encoded file data")
 
-    volume = Int(0, help="""The volume of the video player.""")
+    volume = Int(help="""The volume of the video player.""")
 
 
 class VideoStream(HTMLBox):
diff --git a/panel/package-lock.json b/panel/package-lock.json
index df9e535268..6e506bdb92 100644
--- a/panel/package-lock.json
+++ b/panel/package-lock.json
@@ -20,9 +20,9 @@
       "devDependencies": {}
     },
     "node_modules/@bokeh/bokehjs": {
-      "version": "2.3.0-dev.11",
-      "resolved": "https://registry.npmjs.org/@bokeh/bokehjs/-/bokehjs-2.3.0-dev.11.tgz",
-      "integrity": "sha512-k7IKiYsiHOcQS0UZqzLLzdBucKkmjif5ogMG5pzKp1zR9AKy7SfpB5PPTvfcTasbP3HgLRZdNsLjD3YboPVdRA==",
+      "version": "2.3.0-dev.12",
+      "resolved": "https://registry.npmjs.org/@bokeh/bokehjs/-/bokehjs-2.3.0-dev.12.tgz",
+      "integrity": "sha512-9T1CWvJonH53qe0ZlsL0pHhcQwACqHJ8JT6VipRUl53D2G3/GYYwUdEXxz4Tw4bdjXEFxGMoVSbLOGkgsrWh3g==",
       "dependencies": {
         "@bokeh/numbro": "^1.6.2",
         "@bokeh/slickgrid": "~2.4.2701",
@@ -38,7 +38,6 @@
         "hammerjs": "^2.0.4",
         "nouislider": "^14.6.3",
         "proj4": "^2.6.3",
-        "proxy-polyfill": "^0.3.2",
         "sprintf-js": "^1.1.2",
         "timezone": "^1.0.23",
         "tslib": "^2.0.3",
@@ -46,7 +45,7 @@
       },
       "engines": {
         "node": ">=14",
-        "npm": ">=7.1"
+        "npm": ">=7.4"
       }
     },
     "node_modules/@bokeh/bokehjs/node_modules/tslib": {
@@ -298,11 +297,6 @@
         "wkt-parser": "^1.2.4"
       }
     },
-    "node_modules/proxy-polyfill": {
-      "version": "0.3.2",
-      "resolved": "https://registry.npmjs.org/proxy-polyfill/-/proxy-polyfill-0.3.2.tgz",
-      "integrity": "sha512-ENKSXOMCewnQTOyqrQXxEjIhzT6dy572mtehiItbDoIUF5Sv5UkmRUc8kowg2MFvr232Uo8rwRpNg3V5kgTKbA=="
-    },
     "node_modules/redux": {
       "version": "4.0.5",
       "license": "MIT",
@@ -345,9 +339,9 @@
   },
   "dependencies": {
     "@bokeh/bokehjs": {
-      "version": "2.3.0-dev.11",
-      "resolved": "https://registry.npmjs.org/@bokeh/bokehjs/-/bokehjs-2.3.0-dev.11.tgz",
-      "integrity": "sha512-k7IKiYsiHOcQS0UZqzLLzdBucKkmjif5ogMG5pzKp1zR9AKy7SfpB5PPTvfcTasbP3HgLRZdNsLjD3YboPVdRA==",
+      "version": "2.3.0-dev.12",
+      "resolved": "https://registry.npmjs.org/@bokeh/bokehjs/-/bokehjs-2.3.0-dev.12.tgz",
+      "integrity": "sha512-9T1CWvJonH53qe0ZlsL0pHhcQwACqHJ8JT6VipRUl53D2G3/GYYwUdEXxz4Tw4bdjXEFxGMoVSbLOGkgsrWh3g==",
       "requires": {
         "@bokeh/numbro": "^1.6.2",
         "@bokeh/slickgrid": "~2.4.2701",
@@ -363,7 +357,6 @@
         "hammerjs": "^2.0.4",
         "nouislider": "^14.6.3",
         "proj4": "^2.6.3",
-        "proxy-polyfill": "^0.3.2",
         "sprintf-js": "^1.1.2",
         "timezone": "^1.0.23",
         "tslib": "^2.0.3",
@@ -574,11 +567,6 @@
         "wkt-parser": "^1.2.4"
       }
     },
-    "proxy-polyfill": {
-      "version": "0.3.2",
-      "resolved": "https://registry.npmjs.org/proxy-polyfill/-/proxy-polyfill-0.3.2.tgz",
-      "integrity": "sha512-ENKSXOMCewnQTOyqrQXxEjIhzT6dy572mtehiItbDoIUF5Sv5UkmRUc8kowg2MFvr232Uo8rwRpNg3V5kgTKbA=="
-    },
     "redux": {
       "version": "4.0.5",
       "requires": {
diff --git a/panel/pane/plotly.py b/panel/pane/plotly.py
index 9825373bd3..179142c44e 100644
--- a/panel/pane/plotly.py
+++ b/panel/pane/plotly.py
@@ -214,8 +214,9 @@ def _get_model(self, doc, root=None, parent=None, comm=None):
             properties['sizing_mode'] = 'stretch_both'
 
         model = PlotlyPlot(
-            data=data, layout=layout, config=self.config, data_sources=sources,
-            _render_count=self._render_count, **properties
+            data=data, layout=layout, config=self.config or {},
+            data_sources=sources, _render_count=self._render_count,
+            **properties
         )
 
         if root is None:
diff --git a/panel/pane/vtk/vtk.py b/panel/pane/vtk/vtk.py
index b66cf8252e..e06c75aff4 100644
--- a/panel/pane/vtk/vtk.py
+++ b/panel/pane/vtk/vtk.py
@@ -36,7 +36,7 @@ class AbstractVTK(PaneBase):
 
     __abstract = True
 
-    axes = param.Dict(doc="""
+    axes = param.Dict(default={}, doc="""
         Parameters of the axes to construct in the 3d view.
 
         Must contain at least ``xticker``, ``yticker`` and ``zticker``.
@@ -650,10 +650,10 @@ def _get_model(self, doc, root=None, parent=None, comm=None):
             VTKVolumePlot = getattr(sys.modules['panel.models.vtk'], 'VTKVolumePlot')
 
         props = self._process_param_change(self._init_properties())
-        volume_data = self._volume_data
+        if self._volume_data is not None:
+            props['data'] = self._volume_data
 
-        model = VTKVolumePlot(data=volume_data,
-                              **props)
+        model = VTKVolumePlot(**props)
         if root is None:
             root = model
         self._link_props(model, ['colormap', 'orientation_widget', 'camera', 'mapper', 'controller_expanded'], doc, root, comm)
@@ -820,10 +820,11 @@ def _get_model(self, doc, root=None, parent=None, comm=None):
         else:
             VTKJSPlot = getattr(sys.modules['panel.models.vtk'], 'VTKJSPlot')
 
-        vtkjs = self._get_vtkjs()
-        data = base64encode(vtkjs) if vtkjs is not None else vtkjs
         props = self._process_param_change(self._init_properties())
-        model = VTKJSPlot(data=data, **props)
+        vtkjs = self._get_vtkjs()
+        if vtkjs is not None:
+            props['data'] = base64encode(vtkjs)
+        model = VTKJSPlot(**props)
         if root is None:
             root = model
         self._link_props(model, ['camera', 'enable_keybindings', 'orientation_widget'], doc, root, comm)
diff --git a/panel/tests/test_param.py b/panel/tests/test_param.py
index 02fa2202f7..fe71c90635 100644
--- a/panel/tests/test_param.py
+++ b/panel/tests/test_param.py
@@ -656,14 +656,12 @@ class Test(param.Parameterized):
     assert len(model.children) == 2
     _, number = model.children
 
-    number.value_throttled = 3
+    pane._widgets['a']._process_events({'value_throttled': 3})
     assert number.value != 3
-    assert number.value_throttled == 3
     assert test.a == 3
 
     test.a = 4
     assert number.value != 4
-    assert number.value_throttled == 4
     assert test.a == 4
 
 
diff --git a/panel/tests/widgets/test_select.py b/panel/tests/widgets/test_select.py
index 89aa1aa642..40f1231654 100644
--- a/panel/tests/widgets/test_select.py
+++ b/panel/tests/widgets/test_select.py
@@ -74,7 +74,7 @@ def test_select_change_options(document, comm):
 
     select.options = {}
     assert select.value == None
-    assert widget.value == None
+    assert widget.value == ''
 
 
 def test_select_non_hashable_options(document, comm):
diff --git a/panel/tests/widgets/test_slider.py b/panel/tests/widgets/test_slider.py
index 4aa40aebb0..3e306d7816 100644
--- a/panel/tests/widgets/test_slider.py
+++ b/panel/tests/widgets/test_slider.py
@@ -5,7 +5,6 @@
 
 from bokeh.models import Div as BkDiv, Slider as BkSlider, Column as BkColumn
 
-import param
 from panel.widgets import (DateSlider, DateRangeSlider, DiscreteSlider,
                            FloatSlider, IntSlider, RangeSlider)
 
@@ -22,7 +21,6 @@ def test_float_slider(document, comm):
     assert widget.start == 0.1
     assert widget.end == 0.5
     assert widget.value == 0.4
-    assert widget.value_throttled == 0.4
 
     slider._process_events({'value': 0.2})
     assert slider.value == 0.2
@@ -31,8 +29,6 @@ def test_float_slider(document, comm):
 
     slider.value = 0.3
     assert widget.value == 0.3
-    slider.value_throttled = 0.3
-    assert widget.value_throttled == 0.3
 
 
 def test_int_slider(document, comm):
@@ -47,7 +43,6 @@ def test_int_slider(document, comm):
     assert widget.start == 0
     assert widget.end == 3
     assert widget.value == 1
-    assert widget.value_throttled == 1
 
     slider._process_events({'value': 2})
     assert slider.value == 2
@@ -63,7 +58,6 @@ def test_int_slider(document, comm):
     slider_2 = IntSlider(start=1, end=3, name='Slider_2')
     widget_2 = slider_2.get_root(document, comm=comm)
     assert widget_2.value == widget_2.start
-    assert widget_2.value_throttled == widget_2.start
 
 
 def test_range_slider(document, comm):
@@ -78,7 +72,6 @@ def test_range_slider(document, comm):
     assert widget.start == 0
     assert widget.end == 3
     assert widget.value == (0, 3)
-    assert widget.value_throttled == (0, 3)
 
     slider._process_events({'value': (0, 2)})
     assert slider.value == (0, 2)
@@ -87,8 +80,6 @@ def test_range_slider(document, comm):
 
     slider.value = (0, 1)
     assert widget.value == (0, 1)
-    slider.value_throttled = (0, 1)
-    assert widget.value_throttled == (0, 1)
 
 
 def test_date_slider(document, comm):
@@ -101,7 +92,6 @@ def test_date_slider(document, comm):
     assert isinstance(widget, date_slider._widget_type)
     assert widget.title == 'DateSlider'
     assert widget.value == 1536019200000
-    assert widget.value_throttled == 1536019200000
     assert widget.start == 1535760000000.0
     assert widget.end == 1536537600000.0
 
@@ -109,8 +99,7 @@ def test_date_slider(document, comm):
     widget.value = (datetime(2018, 9, 3)-epoch).total_seconds()*1000
     date_slider._process_events({'value': widget.value})
     assert date_slider.value == date(2018, 9, 3)
-    widget.value_throttled = (datetime(2018, 9, 3)-epoch).total_seconds()*1000
-    date_slider._process_events({'value_throttled': widget.value})
+    date_slider._process_events({'value_throttled': (datetime(2018, 9, 3)-epoch).total_seconds()*1000})
     assert date_slider.value_throttled == date(2018, 9, 3)
 
     # Test raw timestamp value:
@@ -121,8 +110,6 @@ def test_date_slider(document, comm):
 
     date_slider.value = date(2018, 9, 6)
     assert widget.value == 1536192000000
-    date_slider.value_throttled = date(2018, 9, 6)
-    assert widget.value_throttled == 1536192000000
 
 
 def test_date_range_slider(document, comm):
@@ -135,7 +122,6 @@ def test_date_range_slider(document, comm):
     assert isinstance(widget, date_slider._widget_type)
     assert widget.title == 'DateRangeSlider'
     assert widget.value == (1535846400000, 1536019200000)
-    assert widget.value_throttled == (1535846400000, 1536019200000)
     assert widget.start == 1535760000000
     assert widget.end == 1536537600000
 
@@ -144,16 +130,13 @@ def test_date_range_slider(document, comm):
                     (datetime(2018, 9, 6)-epoch).total_seconds()*1000)
     date_slider._process_events({'value': widget.value})
     assert date_slider.value == (datetime(2018, 9, 3), datetime(2018, 9, 6))
-    widget.value_throttled = ((datetime(2018, 9, 3)-epoch).total_seconds()*1000,
+    value_throttled = ((datetime(2018, 9, 3)-epoch).total_seconds()*1000,
                     (datetime(2018, 9, 6)-epoch).total_seconds()*1000)
-    date_slider._process_events({'value_throttled': widget.value_throttled})
+    date_slider._process_events({'value_throttled': value_throttled})
     assert date_slider.value == (datetime(2018, 9, 3), datetime(2018, 9, 6))
 
     date_slider.value = (datetime(2018, 9, 4), datetime(2018, 9, 6))
     assert widget.value == (1536019200000, 1536192000000)
-    date_slider.value_throttled = (datetime(2018, 9, 4), datetime(2018, 9, 6))
-    assert widget.value_throttled == (1536019200000, 1536192000000)
-
 
 
 def test_discrete_slider(document, comm):
@@ -167,7 +150,6 @@ def test_discrete_slider(document, comm):
     assert isinstance(label, BkDiv)
     assert isinstance(widget, BkSlider)
     assert widget.value == 1
-    assert widget.value_throttled == 1
     assert widget.start == 0
     assert widget.end == 3
     assert widget.step == 1
@@ -181,9 +163,6 @@ def test_discrete_slider(document, comm):
 
     discrete_slider.value = 100
     assert widget.value == 3
-    with param.edit_constant(discrete_slider):
-        discrete_slider.value_throttled = 100
-    assert widget.value_throttled == 3
 
 
 def test_discrete_slider_label_update(document, comm):
@@ -211,7 +190,6 @@ def test_discrete_date_slider(document, comm):
     assert isinstance(label, BkDiv)
     assert isinstance(widget, BkSlider)
     assert widget.value == 1
-    assert widget.value_throttled == 1
     assert widget.start == 0
     assert widget.end == 2
     assert widget.step == 1
@@ -225,9 +203,6 @@ def test_discrete_date_slider(document, comm):
 
     discrete_slider.value = dates['2016-01-01']
     assert widget.value == 0
-    with param.edit_constant(discrete_slider):
-        discrete_slider.value_throttled = dates['2016-01-01']
-    assert widget.value_throttled == 0
 
 
 def test_discrete_slider_options_dict(document, comm):
@@ -242,7 +217,6 @@ def test_discrete_slider_options_dict(document, comm):
     assert isinstance(label, BkDiv)
     assert isinstance(widget, BkSlider)
     assert widget.value == 1
-    assert widget.value_throttled == 1
     assert widget.start == 0
     assert widget.end == 3
     assert widget.step == 1
@@ -256,6 +230,3 @@ def test_discrete_slider_options_dict(document, comm):
 
     discrete_slider.value = 100
     assert widget.value == 3
-    with param.edit_constant(discrete_slider):
-        discrete_slider.value_throttled = 100
-    assert widget.value_throttled == 3
diff --git a/panel/widgets/input.py b/panel/widgets/input.py
index 6e237b377f..c9e4960a95 100644
--- a/panel/widgets/input.py
+++ b/panel/widgets/input.py
@@ -256,6 +256,9 @@ class IntInput(_SpinnerBase, _IntInputBase):
 
     value_throttled = param.Integer(default=None, constant=True)
 
+    _rename = dict(_NumericInputBase._rename, value_throttled=None)
+
+
 
 class FloatInput(_SpinnerBase, _FloatInputBase):
 
@@ -263,6 +266,8 @@ class FloatInput(_SpinnerBase, _FloatInputBase):
 
     value_throttled = param.Number(default=None, constant=True)
 
+    _rename = dict(_NumericInputBase._rename, value_throttled=None)
+
 
 class NumberInput(_SpinnerBase):
 
diff --git a/panel/widgets/select.py b/panel/widgets/select.py
index c7e5058774..e72e9062d5 100644
--- a/panel/widgets/select.py
+++ b/panel/widgets/select.py
@@ -73,8 +73,9 @@ def _process_param_change(self, msg):
                 msg['value'] = unicode_values[indexOf(val, values)]
             elif values:
                 self.value = self.values[0]
-            elif self.value is not None:
+            else:
                 self.value = None
+                msg['value'] = ''
 
         if 'options' in msg:
             if isinstance(self.options, dict):
@@ -89,7 +90,7 @@ def _process_param_change(self, msg):
             if values:
                 if not isIn(val, values):
                     self.value = values[0]
-            elif val is not None:
+            else:
                 self.value = None
         return msg
 
@@ -102,8 +103,8 @@ def _process_property_change(self, msg):
         if 'value' in msg:
             if not self.values:
                 pass
-            elif msg['value'] is None:
-                msg['value'] = self.values[0]
+            elif msg['value'] == '':
+                msg['value'] = self.values[0] if self.values else None
             else:
                 if isIn(msg['value'], self.unicode_values):
                     idx = indexOf(msg['value'], self.unicode_values)
diff --git a/panel/widgets/slider.py b/panel/widgets/slider.py
index 17f52a4fc0..d48fcb7044 100644
--- a/panel/widgets/slider.py
+++ b/panel/widgets/slider.py
@@ -118,6 +118,8 @@ class FloatSlider(ContinuousSlider):
 
     step = param.Number(default=0.1)
 
+    _rename = {'name': 'title', 'value_throttled': None}
+
 
 class IntSlider(ContinuousSlider):
 
@@ -131,6 +133,8 @@ class IntSlider(ContinuousSlider):
 
     step = param.Integer(default=1)
 
+    _rename = {'name': 'title', 'value_throttled': None}
+
     def _process_property_change(self, msg):
         msg = super(_SliderBase, self)._process_property_change(msg)
         if 'value' in msg:
@@ -151,6 +155,8 @@ class DateSlider(_SliderBase):
 
     end = param.Date(default=None)
 
+    _rename = {'name': 'title', 'value_throttled': None}
+
     _source_transforms = {'value': None, 'value_throttled': None, 'start': None, 'end': None}
 
     _widget_type = _BkDateSlider
@@ -345,6 +351,8 @@ class RangeSlider(_SliderBase):
 
     step = param.Number(default=0.1)
 
+    _rename = {'name': 'title', 'value_throttled': None}
+
     _widget_type = _BkRangeSlider
 
     def __init__(self, **params):
@@ -400,6 +408,8 @@ class DateRangeSlider(_SliderBase):
     _source_transforms = {'value': None, 'value_throttled': None,
                          'start': None, 'end': None, 'step': None}
 
+    _rename = {'name': 'title', 'value_throttled': None}
+
     _widget_type = _BkDateRangeSlider
 
     def __init__(self, **params):
@@ -408,6 +418,12 @@ def __init__(self, **params):
                                params.get('end', self.end))
         super(DateRangeSlider, self).__init__(**params)
 
+    def _process_param_change(self, msg):
+        msg = super()._process_param_change(msg)
+        if msg.get('value') == (None, None):
+            del msg['value']
+        return msg
+
     def _process_property_change(self, msg):
         msg = super(DateRangeSlider, self)._process_property_change(msg)
         if 'value' in msg:
diff --git a/panel/widgets/tables.py b/panel/widgets/tables.py
index 50f7bc446c..abbacb0d38 100644
--- a/panel/widgets/tables.py
+++ b/panel/widgets/tables.py
@@ -166,8 +166,6 @@ def _get_column_definitions(self, col_names, df):
                 col_kwargs['width'] = self.widths
             elif str(col) in self.widths:
                 col_kwargs['width'] = self.widths.get(str(col))
-            else:
-                col_kwargs['width'] = None
 
             title = self.titles.get(col, str(col))
             if col in indexes and len(indexes) > 1 and self.hierarchical:
diff --git a/setup.py b/setup.py
index 0070222adb..7ededade3c 100644
--- a/setup.py
+++ b/setup.py
@@ -97,7 +97,7 @@ def run(self):
 ########## dependencies ##########
 
 install_requires = [
-    'bokeh >=2.3.0dev11',
+    'bokeh >=2.3.0dev12',
     'param >=1.10.0',
     'pyviz_comms >=0.7.4',
     'markdown',