Trace gRPC hitting Null Pointer on code updates

[isaacrivriv]

During testing, @pnicolucci discovered an issue with trace enabled and HTTP2 where if the pseudoheaders have not been set yet on an H2 request then while writing the response, an NPE can be hit from a trace statement. We need a bit more investigation as to why this is being hit since by the time a response is being sent, I would expect the headers to have already been hit in the request