code: protected void processServerErrorCallback(HttpServletRequest request, HttpServletResponse response, Throwable cause) {
          final RequestServerErrorHandler serverErrorHandler = serverErrorHandlerLocal.get();
          if (serverErrorHandler == null) {
              return;
          }
          try {
              serverErrorHandler.handle(request, response, cause);
          } catch (Throwable handlingEx) {
              final String msg = "Failed to handle '500 Error' by the handler: " + serverErrorHandler;
              if (errorLogging) {
                  logger.error(msg, handlingEx);
              } else {
                  logger.debug(msg, handlingEx);
              }
          }
      }
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