code: @Override
      CssFormatter appendValue( double value, String unit ) {
          if( value == 0 ) {
              switch( unit ) {
                  case "deg":
                  case "s":
                      break;
                  default:
                      super.append( '0' );
                      return this;
              }
          }
          return super.appendValue( value, unit );
      }
docs: Remove units if value is zero.
  {@inheritDoc}