'Get the credit course if exists for the given \'course_key\'.
Args:
course_key(CourseKey): The course identifier
Raises:
DoesNotExist if no CreditCourse exists for the given course key.
Returns:
CreditCourse if one exists for the given course key.'

@classmethod
def get_credit_course(cls, course_key):

    return cls.objects.get(course_key=course_key, enabled=True)
