Significance of `{}` in rpc declarations

Question

While going through the docs of protobufjs and google protobuf official guide I noticed that there is a syntax difference between rpc declarations described by both -

• Google protobuf guide -

    rpc SayHello (HelloRequest) returns (HelloReply)

• ProtobufJS guide -

    rpc SayHello (HelloRequest) returns (HelloReply) {}

Notice the difference in {} at the end.

What is the significance of this ? And does it lead to a different code behavior ?

Reference -

• Google Protobuf guide - https://developers.google.com/protocol-buffers/docs/overview#services
• Protobuf JS Guide - https://protobufjs.github.io/protobuf.js/#using-proto-files