code: public StrBuilder append(final char[] chars) {
          if (chars == null) {
              return appendNull();
          }
          final int strLen = chars.length;
          if (strLen > 0) {
              final int len = length();
              ensureCapacity(len + strLen);
              System.arraycopy(chars, 0, buffer, len, strLen);
              size += strLen;
          }
          return this;
      }
docs: Appends a char array to the string builder.
  Appending null will call {@link #appendNull()}.
  
  @param chars  the char array to append
  @return this, to enable chaining