Accept None in _XfailMarkDecorator's conditionparam and expose default value

AUTHORS

@@ -338,6 +338,7 @@ Saiprasad Kale
 Samuel Colvin
 Samuel Dion-Girardeau
 Samuel Searles-Bryant
+Samuel Therrien (Avasam)
 Samuele Pedroni
 Sanket Duthade
 Sankt Petersbug

changelog/10094#issuecomment-1774215699.improvement.rst

@@ -0,0 +1 @@
+Improved the documentation and type signature for :func:`pytest.mark.xfail <pytest.mark.xfail>`'s ``condition`` param to support ``None``.

doc/en/reference/reference.rst

@@ -239,11 +239,10 @@ Marks a test function as *expected to fail*.
 
 .. py:function:: pytest.mark.xfail(condition=None, *, reason=None, raises=None, run=True, strict=xfail_strict)
 
-    :type condition: bool or str
-    :param condition:
-        Condition for marking the test function as xfail (``True/False`` or a
-        :ref:`condition string <string conditions>`). If a bool, you also have
-        to specify ``reason`` (see :ref:`condition string <string conditions>`).
+    :keyword Optional[Union[bool, str]] condition:
+        Condition for marking the test function as xfail (``True/False/None`` or a
+        :ref:`condition string <string conditions>`). If a bool or None, you also have
+        to specify ``reason`` (see :ref:`condition string <string conditions>`). ``None`` is the same as ``False``.
     :keyword str reason:
         Reason why the test function is marked as xfail.
     :keyword Type[Exception] raises:

src/_pytest/mark/structures.py

@@ -457,8 +457,8 @@ def __call__(self, arg: Markable) -> Markable:
         @overload
         def __call__(
             self,
-            condition: Union[str, bool] = ...,
-            *conditions: Union[str, bool],
+            condition: Optional[Union[str, bool]] = None,
+            *conditions: Optional[Union[str, bool]],
             reason: str = ...,
             run: bool = ...,
             raises: Union[