code: public CharBuffer append (CharSequence csq) {
          if (csq != null) {
              return put(csq.toString());
          }
          return put("null"); //$NON-NLS-1$
      }
docs: Writes all chars of the given character sequence {@code csq} to the current position of
  this buffer, and increases the position by the length of the csq.
  <p> Calling this method has the same effect as {@code append(csq.toString())}. </p>
  If the {@code CharSequence} is {@code null} the string "null" will be written to the buffer.
  
  @param csq the {@code CharSequence} to write.
  @return this buffer.
  @exception BufferOverflowException if {@code remaining()} is less than the length of csq.
  @exception ReadOnlyBufferException if no changes may be made to the contents of this buffer.