code: protected void updateLabelActiveStyle() {
          if (this.valueBoxBase.getText() != null && !this.valueBoxBase.getText().isEmpty()) {
              label.addStyleName(CssName.ACTIVE);
          } else {
              label.removeStyleName(CssName.ACTIVE);
          }
      }
docs: Updates the style of the field label according to the field value if the
  field value is empty - null or "" - removes the label 'active' style else
  will add the 'active' style to the field label.