docs: public static synchronized JingleSession getInstanceFor(XMPPConnection con) {
          if (con == null) {
              throw new IllegalArgumentException("XMPPConnection cannot be null");
          }
  
          JingleSession result = null;
          synchronized (sessions) {
              if (sessions.containsKey(con)) {
                  result = sessions.get(con);
              }
          }
  
          return result;
      }