Document null argument limitation with `SceneTree.call_group()`

doc/classes/SceneTree.xml

@@ -20,6 +20,7 @@
 			<description>
 				Calls [code]method[/code] on each member of the given group. You can pass arguments to [code]method[/code] by specifying them at the end of the method call. This method is equivalent of calling [method call_group_flags] with [constant GROUP_CALL_DEFAULT] flag.
 				[b]Note:[/b] [code]method[/code] may only have 5 arguments at most (7 arguments passed to this method in total).
+				[b]Note:[/b] Due to design limitations, [method call_group] will fail silently if one of the arguments is [code]null[/code].
 				[b]Note:[/b] [method call_group] will always call methods with an one-frame delay, in a way similar to [method Object.call_deferred]. To call methods immediately, use [method call_group_flags] with the [constant GROUP_CALL_REALTIME] flag.
 			</description>
 		</method>
@@ -31,8 +32,10 @@
 			<description>
 				Calls [code]method[/code] on each member of the given group, respecting the given [enum GroupCallFlags]. You can pass arguments to [code]method[/code] by specifying them at the end of the method call.
 				[b]Note:[/b] [code]method[/code] may only have 5 arguments at most (8 arguments passed to this method in total).
+				[b]Note:[/b] Due to design limitations, [method call_group_flags] will fail silently if one of the arguments is [code]null[/code].
 				[codeblock]
-				get_tree().call_group_flags(SceneTree.GROUP_CALL_REALTIME | SceneTree.GROUP_CALL_REVERSE, "bases", "destroy") # Call the method immediately and in reverse order.
+				# Call the method immediately and in reverse order.
+				get_tree().call_group_flags(SceneTree.GROUP_CALL_REALTIME | SceneTree.GROUP_CALL_REVERSE, "bases", "destroy")
 				[/codeblock]
 			</description>
 		</method>