UndoRedo.add_do_method fails when arguments are null

[Jummit]

Godot version:
3.2.4

Issue description:
UndoRedo.add_do_method throws an error:
add_do_method: Condition "action_level <= 0" is true.
<C++ Source> core/undo_redo.cpp:112 @ add_do_method()
if any parameter is null:

func create_action():
	call("multiple_parameters") # fails, not enough arguments
	call("multiple_parameters", null, null) # works

	undo_redo.add_do_method(self, "multiple_parameters") # fails, as expected
	undo_redo.add_do_method(self, "multiple_parameters", null, null) # also fails
	undo_redo.add_do_method(self, "multiple_parameters", null, "some value") # also fails

func multiple_parameters(arg1, arg2):
	pass

Steps to reproduce:
Call UndoRedo.add_do_method with null as one parameter.

[Zylann]

Similar to #36895 ?

[Jummit]

Similar to #36895 ?

Yep :D