code: @Nullable
    public static String extractFullServiceName(String fullMethodName) {
      int index = checkNotNull(fullMethodName, "fullMethodName").lastIndexOf('/');
      if (index == -1) {
        return null;
      }
      return fullMethodName.substring(0, index);
    }
docs: Extract the fully qualified service name out of a fully qualified method name. May return
  {@code null} if the input is malformed, but you cannot rely on it for the validity of the
  input.
  
  @since 1.0.0