Revert "Raise an error when setting None to a base Parameter with `…

…allow_None=False` (#691)" (#712)

This reverts commit 6c995be.

param/parameterized.py

@@ -1255,8 +1255,6 @@ def __set__(self, obj, val):
 
     def _validate_value(self, value, allow_None):
         """Implements validation for parameter value"""
-        if value is None and allow_None is False:
-            raise ValueError("Parameter %r does not accept `None`." % (self.name))
 
     def _validate(self, val):
         """Implements validation for the parameter value and attributes"""

tests/API1/testparameterizedobject.py

@@ -392,30 +392,6 @@ class TestPO1(param.Parameterized):
     x = param.Number(default=numbergen.UniformRandom(lbound=-1,ubound=1,seed=1),bounds=(-1,1))
     y = param.Number(default=1,bounds=(-1,1))
 
-
-class TestParameter(API1TestCase):
-
-    def setUp(self):
-        super(TestParameter, self).setUp()
-
-        class _TestParameter(param.Parameterized):
-            a = param.Parameter(default='')
-            b = param.Parameter(default='',allow_None=True)
-            c = param.Parameter(default=None)
-
-        self._TestParameter = _TestParameter
-
-    def test_handling_of_None(self):
-        t = self._TestParameter()
-
-        with self.assertRaises(ValueError):
-            t.a = None
-
-        t.b = None
-
-        assert t.c is None
-
-
 class TestNumberParameter(API1TestCase):
 
     def test_outside_bounds(self):