.circleci/create_circleci_config.py/CircleCIJob/__post_init__
class CircleCIJob:    def __post_init__(self):
        # Deal with defaults for mutable attributes.
        if self.additional_env is None:
            self.additional_env = {}
        if self.cache_name is None:
            self.cache_name = self.name
        if self.docker_image is None:
            # Let's avoid changing the default list and make a copy.
            self.docker_image = copy.deepcopy(DEFAULT_DOCKER_IMAGE)
        if self.install_steps is None:
            self.install_steps = []
        if self.pytest_options is None:
            self.pytest_options = {}
        if isinstance(self.tests_to_run, str):
            self.tests_to_run = [self.tests_to_run]
        if self.parallelism is None:
            self.parallelism = 1