code: public static ByteBuf copiedBuffer(CharSequence string, Charset charset) {
          if (string == null) {
              throw new NullPointerException("string");
          }
  
          if (string instanceof CharBuffer) {
              return copiedBuffer((CharBuffer) string, charset);
          }
  
          return copiedBuffer(CharBuffer.wrap(string), charset);
      }
docs: Creates a new big-endian buffer whose content is the specified
  {@code string} encoded in the specified {@code charset}.
  The new buffer's {@code readerIndex} and {@code writerIndex} are
  {@code 0} and the length of the encoded string respectively.