code: public static Http2Exception connectionError(Http2Error error, String fmt, Object... args) {
          return new Http2Exception(error, String.format(fmt, args));
      }
docs: Use if an error has occurred which can not be isolated to a single stream, but instead applies
  to the entire connection.
  @param error The type of error as defined by the HTTP/2 specification.
  @param fmt String with the content and format for the additional debug data.
  @param args Objects which fit into the format defined by {@code fmt}.
  @return An exception which can be translated into a HTTP/2 error.