Vaadin Combobox multiselect addon component

I tried to use Combobox Multiselect Vaadin addon Component but I get below error.I have attached demo source code and I follow the link Multiselect dropdown
vaadin.zip (77.6 KB)

Compiling module com.company.vaadin.web.toolkit.ui.AppWidgetSet

Tracing compile failure path for type 'java.util.InternalJsHashCodeMap'
[ERROR] Errors in 'com/google/gwt/emul/java/util/InternalJsHashCodeMap.java'
[ERROR] Line 120: The method elementAdded() is undefined for the type AbstractHashMap<K,V>
[ERROR] Line 137: The method elementRemoved() is undefined for the type AbstractHashMap<K,V>
Tracing compile failure path for type 'java.util.InternalJsStringMap'
[ERROR] Errors in 'com/google/gwt/emul/java/util/InternalJsStringMap.java'
[ERROR] Line 154: The method elementAdded() is undefined for the type AbstractHashMap<K,V>
[ERROR] Line 166: The method elementRemoved() is undefined for the type AbstractHashMap<K,V>
[ERROR] Aborting compile due to errors in some input files
:app-web-toolkit:buildWidgetSet FAILED

FAILURE: Build failed with an exception.

Hi,

Please check if you use correct compatible version of the addon. It should be 1.2.2 because CUBA uses Vaadin 7, not 8: https://vaadin.com/directory/component/comboboxmultiselect-add-on/1.2.2

I am using 1.2.2 version but it is not working

Its working fine, I missed some line in build.gradle file.