code: func CodeGenRequestFieldExtractor(fullMethod string, req interface{}) map[string]interface{} {
  	if ext, ok := req.(requestFieldsExtractor); ok {
  		retMap := make(map[string]interface{})
  		ext.ExtractRequestFields(retMap)
  		if len(retMap) == 0 {
  			return nil
  		}
  		return retMap
  	}
  	return nil
  }
docs: // CodeGenRequestFieldExtractor is a function that relies on code-generated functions that export log fields from requests.
  // These are usually coming from a protoc-plugin that generates additional information based on custom field options.