invalid memory address or nil pointer dereference

Hello,

when i am trying to test manager/state/raft/transport, it fails with :

• go test -buildmode pie -compiler gc -ldflags '-X github.com/docker/swarmkit/version.GitSHA=46ee581f6d737743802fc680d1ba9a7cf0d1465d -extldflags '''-Wl,-z,relro ''''
  time="2018-01-31T12:45:15+01:00" level=error msg="error streaming message to peer" error="rpc error: code = ResourceExhausted desc = trying to send message larger than max (4194309 vs. 4194304)"
  panic: runtime error: invalid memory address or nil pointer dereference
  [signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x5584cb1b6e36]

goroutine 101 [running]:
github.com/docker/swarmkit/manager/state/raft/transport.(*mockRaft).StreamRaftMessage(0xc42006c4e0, 0x5584cb937a20, 0xc4200718d0, 0x5584cb932b60, 0xc42006c4e0)
/builddir/build/BUILD/swarmkit-46ee581f6d737743802fc680d1ba9a7cf0d1465d/_build/src/github.com/docker/swarmkit/manager/state/raft/transport/mock_raft_test.go:138 +0x476
github.com/docker/swarmkit/api._Raft_StreamRaftMessage_Handler(0x5584cb5f1c20, 0xc42006c4e0, 0x5584cb936b80, 0xc4201beb40, 0xc4204bcc00, 0xc4204bccc0)
/builddir/build/BUILD/swarmkit-46ee581f6d737743802fc680d1ba9a7cf0d1465d/_build/src/github.com/docker/swarmkit/api/raft.pb.go:963 +0xb4
google.golang.org/grpc.(*Server).processStreamingRPC(0xc4200ea280, 0x5584cb937780, 0xc42006be00, 0xc4209a6500, 0xc42016b260, 0x5584cb9178a0, 0xc420a0a9f0, 0x0, 0x0)
/usr/share/gocode/src/google.golang.org/grpc/server.go:891 +0x945
google.golang.org/grpc.(*Server).handleStream(0xc4200ea280, 0x5584cb937780, 0xc42006be00, 0xc4209a6500, 0xc420a0a9f0)
/usr/share/gocode/src/google.golang.org/grpc/server.go:985 +0x14c3
google.golang.org/grpc.(*Server).serveStreams.func1.1(0xc4200181b0, 0xc4200ea280, 0x5584cb937780, 0xc42006be00, 0xc4209a6500)
/usr/share/gocode/src/google.golang.org/grpc/server.go:551 +0xa1
created by google.golang.org/grpc.(*Server).serveStreams.func1
/usr/share/gocode/src/google.golang.org/grpc/server.go:549 +0xa3
exit status 2

thanks you for your help

Reproduce the failure with the manager/state/raft/transport tests and inspect manager/state/raft/transport/mock_raft_test.go at line 138, where the nil dereference occurs. Trace the oversized-message error through the gRPC stream and determine the expected test behavior. Done means the test completes without a panic while handling the reported ResourceExhausted error.