@NotNull
    @Override
    public TreeViewer getNavigatorViewer()
    {
        return tree.getViewer();
    }
Navigator nodes filter.
Implementation returns true if element shouldn't be filtered (i.e. always visible).
@return filter or null if no filtering is supported.
plugins/org.jkiss.dbeaver.ui.navigator/src/org/jkiss/dbeaver/ui/navigator/database/NavigatorViewBase.java