'returns the course module associated with the course_id. If no such course exists,
it returns None
:param course_key: must be a CourseKey'

@strip_key
def get_course(self, course_key, depth=0, **kwargs):

    assert isinstance(course_key, CourseKey)
    store = self._get_modulestore_for_courselike(course_key)
    try:
        return store.get_course(course_key, depth=depth, **kwargs)
    except ItemNotFoundError:
        return None
