code: public static synchronized <T extends Exception> void exception(Class<T> exception, ErrorHandler<T> handler) {
          checkStarted();
          instance().exceptionMapper.put(exception, handler);
      }
docs: Register an error interceptor that captures original thrown from endpoints, allowing to change the http response.
  The default response is mapped to any {@link Exception} and returns an {@link HttpException} body
  
  @param <T> The exception type
  @param exception The original type that will trigger the handler
  @param handler   The handler that handles the original and send the appropriate response.