clear() on a Select does not clear the value

[FrankHossfeld]

To reproduce the error:

• create a Select widget
• call clear

Value is not clear.

I'll add the code where I use the clear:

   this.natuerlichePerson = SwitchButton.create(ApplicationConstantsFactory.INSTANCE.get("natuerlichePerson"),
                                                 ApplicationConstantsFactory.INSTANCE.get("no"),
                                                 ApplicationConstantsFactory.INSTANCE.get("yes"))
                                         .groupBy(grouping)
                                         .addChangeListener((oldValue, newValue) -> {
                                           if (newValue) {
                                             this.gesellschaftsform.clear();
                                             this.gesellschaftsform.hide();
                                             this.gesellschaftsform.setRequired(false);
                                           } else {
                                             this.gesellschaftsform.show();
                                             this.gesellschaftsform.setRequired(true);
                                           }
                                         });

    this.gesellschaftsform = Select.<String>create(ApplicationConstantsFactory.INSTANCE.get("gesellschaftsform"))
                                   .groupBy(grouping)
                                   .setRequired(true);
    List<SelectOption<String>> optionsList = new ArrayList<>();
    Arrays.asList(ClGesellschaftsform.values())
          .forEach(e -> optionsList.add(SelectOption.create(e.getKurzBezeichnung(),
                                                            e.getKurzBezeichnung(),
                                                            e.getBezeichnung())));
    optionsList.forEach(o -> this.gesellschaftsform.appendChild(o));

Expected result should be that the clear()-call should deselect a choosen value/ clears the selection.