from typing import overload
@overload
def foo(x: int) -> None: ...
@overload
def foo(x: str) -> None: ...
@overload
def foo(x: bytes) -> None: ...
@overload
def foo(x: bytearray) -> None: ...
def foo(x): return None
def main() -> None: foo(None)

$ mypy foo.py 
foo.py:9: error: Overloaded function signature 4 will never be matched: signature 3's parameter type(s) are the same or broader
foo.py:11: error: No overload variant of "foo" matches argument type "None"
foo.py:11: note: Possible overload variants:
foo.py:11: note:     def foo(x: int) -> None
foo.py:11: note:     def foo(x: str) -> None
foo.py:11: note:     <2 more similar overloads not shown, out of 4 total overloads>
Found 2 errors in 1 file (checked 1 source file)
$ mypy -vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv foo.py 2>&1 | grep 'def foo'
foo.py:11: note:     def foo(x: int) -> None
foo.py:11: note:     def foo(x: str) -> None

$ mypy --version
mypy 0.782
$ head -1 `which mypy`
#!/home/akuli/.local/bin/python3.8