code: public static void setCallbackContextOnThread(SMailCallbackContext callbackContext) {
          if (callbackContext == null) {
              String msg = "The argument 'callbackContext' must not be null.";
              throw new IllegalArgumentException(msg);
          }
          getActiveHolder().save(callbackContext);
      }
docs: Set callback context on thread. <br>
  You can use setting methods per interface instead of this method.
  @param callbackContext The context of callback. (NotNull)