docs: def ison(self, nicks):
          """
          Checks if a nick is on or not.
          Returns list of nicks online.
          Required arguments:
          * nick - Nick to check.
          """
          with self.lock:
              self.send('ISON :%s' % ' '.join(nicks))
              online_nicks = []
              if self.readable():
                  msg = self._recv(expected_replies=('303',))
                  if msg[0] == '303':
                      online_nicks = msg[2].replace(':', '', 1).split()
              return online_nicks