Treat thenAnswer() to return None

Revert fbb9a5f (Do not allow a bare `thenAnswer()`) which was never
released.

Author: kaste

mockito/invocation.py

@@ -532,9 +532,7 @@ def thenRaise(self, *exceptions: Exception | type[Exception]) -> Self:
         return self
 
     def thenAnswer(self, *callables: Callable) -> Self:
-        if not callables:
-            raise TypeError("No answer function provided")
-        for callable in callables:
+        for callable in callables or (return_(None),):
             answer = callable
             if self.discard_first_arg:
                 answer = discard_self(answer)

tests/when_interface_test.py

@@ -47,11 +47,11 @@ def testAssumeReturnNoneIfOmitted(self):
         assert dog.bark() is None
         assert dog.bark() == 42
 
-    def testRaiseIfAnswerIsOmitted(self):
+    def testAssumeReturnNoneIfAnswerIsOmitted(self):
         dog = Dog()
-        with pytest.raises(TypeError) as exc:
-            when(dog).bark().thenAnswer()
-        assert str(exc.value) == "No answer function provided"
+        when(dog).bark().thenAnswer().thenReturn(42)
+        assert dog.bark() is None
+        assert dog.bark() == 42
 
     def testAssumeRaiseExceptionIfOmitted(self):
         dog = Dog()