<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def endpoint_from_flag(flag):
 """The object used for interacting with relations tied to a flag, or None. """

    relation_name = None
    value = _get_flag_value(flag)
    if isinstance(value, dict) and 'relation' in value:
        # old-style RelationBase
        relation_name = value['relation']
    elif flag.startswith('endpoint.'):
        # new-style Endpoint
        relation_name = flag.split('.')[1]
    elif '.' in flag:
        # might be an unprefixed new-style Endpoint
        relation_name = flag.split('.')[0]
        if relation_name not in hookenv.relation_types():
            return None
    if relation_name:
        factory = relation_factory(relation_name)
        if factory:
            return factory.from_flag(flag)
    return None