code: protected String eval(final Object[] _values)
      {
          final String ret;
          if ((_values == null) || (_values.length == 0) || (_values[0] == null))  {
              ret = null;
          } else if (_values[0] instanceof String) {
              ret = (String) _values[0];
          } else if (_values[0] != null) {
              ret = _values[0].toString();
          } else  {
              ret = null;
          }
          return ret;
      }
docs: The localized string and the internal string value are equal. So the
  internal value can be set directly with method {@link #setValue}.
  
  @param _values   values to evaluate
  @return string representation for the <code>_values</code>