code: @Override
      public String validateValue(final UIValue _value)
      {
          String ret = null;
          try {
              if (_value.getDbValue() != null) {
                  Long.valueOf(String.valueOf(_value.getDbValue()));
              }
          } catch (final NumberFormatException e) {
              ret = DBProperties.getProperty(NumberUI.class.getName() + ".InvalidValue");
          }
          return ret;
      }
docs: {@inheritDoc}