WorkbenchField.initContent() calls this.view.setViewType(TreePresenterDefinition.VIEW_TYPE);
to initialize default view to tree, but when workbench doesn't have a tree and only list or only thumbnails view is configured, this call ends up in WorkbenchViewImpl.setViewType() which does

        final Component c = contentViews.get(type).asVaadinComponent();

... and since tree type is not in the list of views it fails w/ NPE.

It should either signal back to field that request can't be fulfilled, or field should check for existence of tree before trying to set it or there should be some fallback to first available view or ...