code: public JingleSession getSession(String jid) {
          for (JingleSession jingleSession : jingleSessions) {
              if (jingleSession.getResponder().equals(jid)) {
                  return jingleSession;
              }
          }
          return null;
      }
docs: Get a session with the informed JID. If no session is found, return null.
  
  @param jid
  @return the JingleSession