title: How to print all protobuf fields in gRPC response, even when empty
body: <p>I'm writing a gRPC service with a protobuf definition as follows:</p>
  <pre><code>message MyRequest {
  }
  
  message MyResponse {
    string username = 1;
    repeated string schools = 3;
  }
  
  service MyService {
    rpc Service(MyRequest) returns (MyResponse) {}
  }
  </code></pre>
  <p>The service returns a list of schools for the current user. Sometimes there will be no schools for a user, and I want the response in the <code>schools</code> field to be an empty list, but instead the field is just missing from the response.</p>
  <p>What do I need to do to get the <code>schools</code> field to always be present in the response, even when it's an empty list?</p>