<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def decode_link(self, link):
 """ Decodes an RpbLink message into a tuple :param link: an RpbLink message :type link: riak.pb.riak_pb2.RpbLink :rtype tuple """


        if link.HasField("bucket"):
            bucket = bytes_to_str(link.bucket)
        else:
            bucket = None
        if link.HasField("key"):
            key = bytes_to_str(link.key)
        else:
            key = None
        if link.HasField("tag"):
            tag = bytes_to_str(link.tag)
        else:
            tag = None

        return (bucket, key, tag)