GWT TypeError by Mouse over on Grid

vaadin 8.0.5, spring-boot 1.5.2.RELEASE

protected void init(VaadinRequest request) {
Grid<SelectionElement> grid = new Grid<>("Title");
         grid.addColumn(SelectionElement::getValue);
        grid.addColumn(SelectionElement::getCount);
        ArrayList<SelectionElement> items = new ArrayList<>();

        items.add(new SelectionElement("Entry-1", 5));
        items.add(new SelectionElement("Entry-2", 15));

        grid.setItems(items);
        setContent(grid);
}

public class SelectionElement implements Comparable<SelectionElement> {

    private Long count;
    private Object value;

...

ERROR on browser console:
com.vaadin.client.ApplicationConfigurationSEVERE: (TypeError) : Cannot read property 'a' of nullcom.google.gwt.core.client.JavaScriptException: (TypeError) : Cannot read property 'a' of null    at Unknown.DDd(AppWidgetset-0.js)    at Unknown.eNd(AppWidgetset-0.js)    at Unknown.ZAb(AppWidgetset-0.js)    at Unknown.HCb(AppWidgetset-0.js)    at Unknown.Gi(AppWidgetset-0.js)    at Unknown.Ji(AppWidgetset-0.js)    at Unknown.eval(AppWidgetset-0.js)

dependencies of of addon-

<dependencies>    
        <dependency>
            <groupId>com.vaadin</groupId>
            <artifactId>vaadin-compatibility-client</artifactId>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>org.vaadin.addon</groupId>
            <artifactId>easyuploads</artifactId>
            <version>8.0.0</version>
        </dependency>

        <dependency>
            <groupId>com.vaadin.tapio</groupId>
            <artifactId>googlemaps</artifactId>
            <version>2.0.0</version>
        </dependency>
        <dependency>
            <groupId>org.vaadin.addons</groupId>
            <artifactId>vaadin-jcrop</artifactId>
            <version>1.2.0</version>
        </dependency>
        <dependency>
            <groupId>com.wcs.wcslib</groupId>
            <artifactId>wcslib-vaadin-widget-recaptcha</artifactId>
            <version>2.0.2</version>
        </dependency>
    </dependencies>

dependencies of ui-project

<dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>com.vaadin</groupId>
            <artifactId>vaadin-push</artifactId>
        </dependency>
        <dependency>
            <groupId>com.vaadin</groupId>
            <artifactId>vaadin-compatibility-server</artifactId>
        </dependency>
        <dependency>
            <groupId>com.vaadin</groupId>
            <artifactId>vaadin-themes</artifactId>
        </dependency>
        <dependency>
            <groupId>com.vaadin</groupId>
            <artifactId>vaadin-spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>com.vaadin</groupId>
            <artifactId>vaadin-compatibility-client-compiled</artifactId>
        </dependency>
        <dependency>
            <groupId>com.vaadin</groupId>
            <artifactId>vaadin-compatibility-client</artifactId>
        </dependency>

correctur: its not mouse over all Grid. just on

<tr class="v-grid-row v-grid-row-focused v-grid-row-has-data" style="width: 1280px; transform: translate3d(0px, 0px, 0px);">

for mouse over and out