NullPointer when releasing frame

I'm see this error complaining about not being able to release a frame

```
 2018-07-23 11:25:56,340 WARN i.n.u.ReferenceCountUtil [parallel-8] Failed to release a message: [!!!io.rsocket.Frame@451cc36f=>java.lang.NullPointerException:null!!!]
java.lang.NullPointerException: null
```