MaterialTree: NullPointerException when deselectSelectedItem execute

[xkazama-yukio3]

I use MaterialTree.

I thought that I wanted to manually cancel selected state in MaterialTree,
I attempted to use MaterialTree#deselectSelectedItem() (added from #163)
When execute, NullPointer has occurred.

Reason:
By SelectionEvent (selectedItem = null) fired in the deselectSelectedItem method,
it occurs in SelectionHandler that is set by MaterialTree itself.

Need a null check in SelectionHandler?

for (Widget item : getChildren()) {
    if (item instanceof MaterialTreeItem) {
        clearSelectedStyles((MaterialTreeItem) item);
    }
}
MaterialTreeItem treeItem = event.getSelectedItem();
// Add Check whether tree has selected item
if (treeItem != null) {
	treeItem.addStyleName(AddinsCssName.SELECTED);
}
setSelectedItem(treeItem);

[kevzlou7979]

You are right, this will also trigger a nullpointerexception. Thanks for the catch will be patching this out.

[kevzlou7979]

Fixed via 6f585ff