<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def tags(tag_references):
 """Returns a formatted list of tags."""

    if not tag_references:
        return blank()

    tag_row = []
    for tag_detail in tag_references:
        tag = utils.lookup(tag_detail, 'tag', 'name')
        if tag is not None:
            tag_row.append(tag)

    return listing(tag_row, separator=', ')