NsContentNameList : NsContentName
                      | NsContentNameList COMMA NsContentName

def p_NsContentNameList(p):
    '''
    NsContentNameList : NsContentName
                      | NsContentNameList COMMA NsContentName
    '''
    if len(p) == 2:
        p[0] = NsContentNameList(None, p[1])
    else:
        p[0] = NsContentNameList(p[1], p[3])