code: public void append(final CharArrayBuffer b, final int off, final int len) {
          if (b == null) {
              return;
          }
          append(b.array, off, len);
      }
docs: Appends {@code len} chars to this buffer from the given source
  buffer starting at index {@code off}. The capacity of the
  destination buffer is increased, if necessary, to accommodate all
  {@code len} chars.
  
  @param   b        the source buffer to be appended.
  @param   off      the index of the first char to append.
  @param   len      the number of chars to append.
  @throws IndexOutOfBoundsException if {@code off} is out of
  range, {@code len} is negative, or
  {@code off} + {@code len} is out of range.