Performs a pop and coerces to a bool.

def pop_bool(self, key: str, default: Any = DEFAULT) -> bool:
        """
        Performs a pop and coerces to a bool.
        """
        value = self.pop(key, default)
        if value is None:
            return None
        elif isinstance(value, bool):
            return value
        elif value == "true":
            return True
        elif value == "false":
            return False
        else:
            raise ValueError("Cannot convert variable to bool: " + value)