apache/hadoop · error · ServiceException

null param while calling Method: [{}]

Error message

null param while calling Method: [{}]

What it means

ProtobufRpcEngine2's InvocationHandler rejects a null request message (args[1] == null) with ServiceException('null param while calling Method: [m]') because protobuf messages cannot be null on the wire — there is always at least a default instance. Thrown client-side, before a connection is made.

Source

Thrown at hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/ProtobufRpcEngine2.java:236

     * cause is RemoteException, then unwrap it to get the exception thrown by
     * the server.
     */
    @Override
    public Message invoke(Object proxy, final Method method, Object[] args)
        throws ServiceException {
      long startTime = 0;
      if (LOG.isDebugEnabled()) {
        startTime = Time.monotonicNow();
      }

      if (args.length != 2) { // RpcController + Message
        throw new ServiceException(
            "Too many or few parameters for request. Method: ["
            + method.getName() + "]" + ", Expected: 2, Actual: "
            + args.length);
      }
      if (args[1] == null) {
        throw new ServiceException("null param while calling Method: ["
            + method.getName() + "]");
      }

      // if Tracing is on then start a new span for this rpc.
      // guard it in the if statement to make sure there isn't
      // any extra string manipulation.
      Tracer tracer = Tracer.curThreadTracer();
      TraceScope traceScope = null;
      if (tracer != null) {
        traceScope = tracer.newScope(RpcClientUtil.methodToTraceString(method));
      }

      if (LOG.isTraceEnabled()) {
        LOG.trace(Thread.currentThread().getId() + ": Call -> " +
            remoteId + ": " + method.getName() +
            " {" + TextFormat.shortDebugString((Message) args[1]) + "}");
      }

View on GitHub (pinned to 2add963021)

Solutions

1. Pass Message.getDefaultInstance() for 'empty' requests.
2. Make request-builder helpers never return null — throw or return the default instance.
3. Add Objects.requireNonNull(request) at the wrapper boundary for a clearer failure.

Example fix

// before
proxy.rename(null, null); // null request -> ServiceException

// after
proxy.rename(null,
    RenameRequestProto.newBuilder()
        .setSrc("/a").setDst("/b").build());

java.util.Objects.requireNonNull(request,
    "protobuf request for " + method.getName() + " must not be null; use getDefaultInstance() if empty");

When it happens

Trigger: Calling proxy.method(controller, null); a request-builder helper returning null on validation failure and being forwarded; argument-order mix-ups where null lands in the message slot.

Common situations: Test harnesses stubbing request construction; wrapper APIs with optional parameters defaulted to null; refactors from WritableRpcEngine (where null params were sometimes tolerated) to protobuf.

Related errors

• null param while calling Method: [{}]
• Null protocol
• Too many or few parameters for request. Method: [{}], Expect
• Unknown method {} called on {} protocol.
• Too many or few parameters for request. Method: [{}], Expect

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/6929c98a471918d7. Report an issue: GitHub.