docs: @GwtIncompatible("Writer")
    static CharOutput asCharOutput(final Writer writer) {
      checkNotNull(writer);
      return new CharOutput() {
        @Override
        public void write(char c) throws IOException {
          writer.append(c);
        }
  
        @Override
        public void flush() throws IOException {
          writer.flush();
        }
  
        @Override
        public void close() throws IOException {
          writer.close();
        }
      };
    }