public static void addContextMenu(final IWorkbenchSite workbenchSite, final Viewer viewer) {
        addContextMenu(workbenchSite, viewer, viewer);
    }
Find selected node for specified UI element
@param element ui element
@return node or null
plugins/org.jkiss.dbeaver.ui.navigator/src/org/jkiss/dbeaver/ui/navigator/NavigatorUtils.java