code: public static void append(File file, Reader reader, String charset) throws IOException {
          append(file, reader, charset, false);
      }
docs: Append the text supplied by the Reader at the end of the File
  without writing a BOM, using a specified encoding.
  
  @param file    a File
  @param reader  the Reader supplying the text to append at the end of the File
  @param charset the charset used
  @throws IOException if an IOException occurs.
  @since 2.3