/*
 *  Licensed to the Apache Software Foundation (ASF) under one
 *  or more contributor license agreements.  See the NOTICE file
 *  distributed with this work for additional information
 *  regarding copyright ownership.  The ASF licenses this file
 *  to you under the Apache License, Version 2.0 (the
 *  "License"); you may not use this file except in compliance
 *  with the License.  You may obtain a copy of the License at
 *
 *        http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing,
 *  software distributed under the License is distributed on an
 *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 *  KIND, either express or implied.  See the License for the
 *  specific language governing permissions and limitations
 *  under the License.
 */
package org.apache.isis.viewer.wicket.ui.components.widgets.select2;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;

import org.apache.wicket.model.IModel;
import org.wicketstuff.select2.Select2MultiChoice;

import org.apache.isis.core.commons.internal.base._Casts;
import org.apache.isis.core.metamodel.spec.ObjectSpecId;
import org.apache.isis.core.webapp.context.memento.ObjectMemento;
import org.apache.isis.viewer.wicket.model.models.ScalarModel;
import org.apache.isis.viewer.wicket.ui.components.widgets.select2.providers.EmptyChoiceProvider;

import lombok.val;

public class Select2MultiChoiceExt
extends Select2MultiChoice<ObjectMemento>
implements ChoiceExt {

    private static final long serialVersionUID = 1L;

    public static Select2MultiChoiceExt create(
            final String id,
            final IModel<ArrayList<ObjectMemento>> modelObject,
            final ScalarModel scalarModel) {
        
        return new Select2MultiChoiceExt(id, _Casts.uncheckedCast(modelObject), scalarModel);
    }

    private final ObjectSpecId specId;

    Select2MultiChoiceExt(
            final String id,
            final IModel<Collection<ObjectMemento>> model,
            final ScalarModel scalarModel) {
        
        super(id, model, EmptyChoiceProvider.INSTANCE);
        specId = scalarModel.getTypeOfSpecification().getSpecId();

        getSettings().setCloseOnSelect(true);

        setOutputMarkupPlaceholderTag(true);
    }

    @Override
    public ObjectSpecId getSpecId() {
        return specId;
    }
    
    
    @Override
    public void updateModel() {
        super.updateModel();
    }
    
    @Override
    public Collection<ObjectMemento> getModelObject() {
        val modelObj = super.getModelObject();
        return modelObj==null
                ? Collections.emptyList() 
                : new ArrayList<>(modelObj);
    }
    
}

@@ -949,38 +949,8 @@
 ion;
-%0Aimport java.util.Collections;
 %0A%0Aim
@@ -1890,16 +1890,21 @@
  specId;
+%0A    
 %0A%0A    Se
@@ -2371,24 +2371,135 @@
 %0A    %7D%0A    %0A
+    // -- bug in wicket 8.8.0 -------------------------------------------%0A    %0A    private boolean workaround;%0A
     %0A    @Ov
@@ -2533,24 +2533,51 @@
 teModel() %7B%0A
+        workaround = true;%0A
         supe
@@ -2589,24 +2589,52 @@
 ateModel();%0A
+        workaround = false;%0A
     %7D%0A    %0A 
@@ -2745,24 +2745,53 @@
 elObject();%0A
+        if(workaround) %7B%0A    
         retu
@@ -2828,35 +2828,24 @@
     
-? Collections.emptyList() %0A
+    ? null %0A    
     
@@ -2884,22 +2884,140 @@
 delObj);
-%0A    %7D
+    %0A        %7D%0A        return modelObj;%0A    %7D%0A    %0A    // ------------------------------------------------------------------
 %0A    %0A%7D%0A

make the workaround as side-effect free as possible