diff --git a/CHANGES.rst b/CHANGES.rst
index 761d251b..bdbc544b 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -1,6 +1,10 @@
 platformdirs Changelog
 ======================
 
+platformdirs 2.2.0
+------------------
+- Unix: Fallback to default if XDG environment variable is empty
+
 platformdirs 2.1.0
 ------------------
 - Add ``readthedocs.org`` documentation via Sphinx
diff --git a/src/platformdirs/unix.py b/src/platformdirs/unix.py
index 02beca29..3f6afec5 100644
--- a/src/platformdirs/unix.py
+++ b/src/platformdirs/unix.py
@@ -22,9 +22,8 @@ def user_data_dir(self) -> str:
         :return: data directory tied to the user, e.g. ``~/.local/share/$appname/$version`` or
          ``$XDG_DATA_HOME/$appname/$version``
         """
-        if "XDG_DATA_HOME" in os.environ:
-            path = os.environ["XDG_DATA_HOME"]
-        else:
+        path = os.environ.get("XDG_DATA_HOME", "")
+        if not path.strip():
             path = os.path.expanduser("~/.local/share")
         return self._append_app_name_and_version(path)
 
@@ -36,9 +35,8 @@ def site_data_dir(self) -> str:
          path separator), e.g. ``/usr/local/share/$appname/$version`` or ``/usr/share/$appname/$version``
         """
         # XDG default for $XDG_DATA_DIRS; only first, if multipath is False
-        if "XDG_DATA_DIRS" in os.environ:
-            path = os.environ["XDG_DATA_DIRS"]
-        else:
+        path = os.environ.get("XDG_DATA_DIRS", "")
+        if not path.strip():
             path = f"/usr/local/share{os.pathsep}/usr/share"
         return self._with_multi_path(path)
 
@@ -55,9 +53,8 @@ def user_config_dir(self) -> str:
         :return: config directory tied to the user, e.g. ``~/.config/$appname/$version`` or
          ``$XDG_CONFIG_HOME/$appname/$version``
         """
-        if "XDG_CONFIG_HOME" in os.environ:
-            path = os.environ["XDG_CONFIG_HOME"]
-        else:
+        path = os.environ.get("XDG_CONFIG_HOME", "")
+        if not path.strip():
             path = os.path.expanduser("~/.config")
         return self._append_app_name_and_version(path)
 
@@ -69,9 +66,8 @@ def site_config_dir(self) -> str:
          path separator), e.g. ``/etc/xdg/$appname/$version``
         """
         # XDG default for $XDG_CONFIG_DIRS only first, if multipath is False
-        if "XDG_CONFIG_DIRS" in os.environ:
-            path = os.environ["XDG_CONFIG_DIRS"]
-        else:
+        path = os.environ.get("XDG_CONFIG_DIRS", "")
+        if not path.strip():
             path = "/etc/xdg"
         return self._with_multi_path(path)
 
@@ -81,9 +77,8 @@ def user_cache_dir(self) -> str:
         :return: cache directory tied to the user, e.g. ``~/.cache/$appname/$version`` or
          ``~/$XDG_CACHE_HOME/$appname/$version``
         """
-        if "XDG_CACHE_HOME" in os.environ:
-            path = os.environ["XDG_CACHE_HOME"]
-        else:
+        path = os.environ.get("XDG_CACHE_HOME", "")
+        if not path.strip():
             path = os.path.expanduser("~/.cache")
         return self._append_app_name_and_version(path)
 
@@ -93,9 +88,8 @@ def user_state_dir(self) -> str:
         :return: state directory tied to the user, e.g. ``~/.local/state/$appname/$version`` or
          ``$XDG_STATE_HOME/$appname/$version``
         """
-        if "XDG_STATE_HOME" in os.environ:
-            path = os.environ["XDG_STATE_HOME"]
-        else:
+        path = os.environ.get("XDG_STATE_HOME", "")
+        if not path.strip():
             path = os.path.expanduser("~/.local/state")
         return self._append_app_name_and_version(path)
 
diff --git a/tests/test_unix.py b/tests/test_unix.py
new file mode 100644
index 00000000..59e60e60
--- /dev/null
+++ b/tests/test_unix.py
@@ -0,0 +1,51 @@
+import os
+import typing
+
+import pytest
+from _pytest.monkeypatch import MonkeyPatch
+
+from platformdirs.unix import Unix
+
+
+class XDGVariable(typing.NamedTuple):
+    name: str
+    default_value: str
+
+
+def _func_to_path(func: str) -> XDGVariable:
+    mapping = {
+        "user_data_dir": XDGVariable("XDG_DATA_HOME", "~/.local/share"),
+        "site_data_dir": XDGVariable("XDG_DATA_DIRS", f"/usr/local/share{os.pathsep}/usr/share"),
+        "user_config_dir": XDGVariable("XDG_CONFIG_HOME", "~/.config"),
+        "site_config_dir": XDGVariable("XDG_CONFIG_DIRS", "/etc/xdg"),
+        "user_cache_dir": XDGVariable("XDG_CACHE_HOME", "~/.cache"),
+        "user_state_dir": XDGVariable("XDG_STATE_HOME", "~/.local/state"),
+        "user_log_dir": XDGVariable("XDG_CACHE_HOME", "~/.cache"),
+    }
+    return mapping[func]
+
+
+@pytest.fixture()
+def dirs_instance() -> Unix:
+    return Unix(multipath=True, opinion=False)
+
+
+def test_xdg_variable_not_set(monkeypatch: MonkeyPatch, dirs_instance: Unix, func: str) -> None:
+    xdg_variable = _func_to_path(func)
+    monkeypatch.delenv(xdg_variable.name, raising=False)
+    result = getattr(dirs_instance, func)
+    assert result == os.path.expanduser(xdg_variable.default_value)
+
+
+def test_xdg_variable_empty_value(monkeypatch: MonkeyPatch, dirs_instance: Unix, func: str) -> None:
+    xdg_variable = _func_to_path(func)
+    monkeypatch.setenv(xdg_variable.name, "")
+    result = getattr(dirs_instance, func)
+    assert result == os.path.expanduser(xdg_variable.default_value)
+
+
+def test_xdg_variable_custom_value(monkeypatch: MonkeyPatch, dirs_instance: Unix, func: str) -> None:
+    xdg_variable = _func_to_path(func)
+    monkeypatch.setenv(xdg_variable.name, "/tmp/custom-dir")
+    result = getattr(dirs_instance, func)
+    assert result == "/tmp/custom-dir"
diff --git a/whitelist.txt b/whitelist.txt
index 7428da1c..c390319a 100644
--- a/whitelist.txt
+++ b/whitelist.txt
@@ -12,13 +12,11 @@ Dirs
 func
 highbit
 HKEY
-impl
 intersphinx
 isfunction
 jnius
 kernel32
 lru
-macos
 multipath
 normpath
 ord
@@ -28,7 +26,6 @@ pathlib
 pathsep
 platformdirs
 pyjnius
-Runtime
 setenv
 shell32
 typehints