from typing import Union, Optional


class Foo:
    ...
    
    
class Bar(Foo):
    ...
    
    
class Thing:
    thing: Optional[Foo]
    
    def errors(self, x: Union[bool, Foo]) -> None:
        if x is True:
            self.thing = Bar()
        elif x is False:
            self.thing = None
        else:
            self.thing = x
            
    def works(self, x: Union[bool, Foo]) -> None:
        if isinstance(x, bool):
            self.thing = Bar() if x else None
        else:
            self.thing = x

main.py:21: error: Incompatible types in assignment (expression has type "Union[bool, Foo]", variable has type "Optional[Foo]")
Found 1 error in 1 file (checked 1 source file)