<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def is_installed(self, name: str) -> bool: """ Indicates a given Docker image is installed on this server. Parameters: name: the name of the Docker image. Returns: `True` if installed; `False` if not. """

        assert name is not None
        try:
            self.__docker.images.get(name)
            return True
        except docker.errors.ImageNotFound:
            return False