code: public static void setDebuggerClass(Class<? extends SmackDebugger> debuggerClass) {
          if (debuggerClass == null) {
              System.clearProperty(DEBUGGER_CLASS_PROPERTY_NAME);
          } else {
              System.setProperty(DEBUGGER_CLASS_PROPERTY_NAME, debuggerClass.getCanonicalName());
          }
      }
docs: Sets custom debugger class to be created by this factory.
  @param debuggerClass class to be used by this factory