@Override
        protected void onSelectAll(final CellPreviewEvent<DocumentType> e) {
            toggleSelectAll();
            refreshView();
            DataSelectionEvent.fire(
                    TypeFilterPresenter.this,
                    TypeFilterPresenter.this,
                    false);
        }
@return A set of types to include, or empty if the type filter is not active
stroom-core-client/src/main/java/stroom/explorer/client/presenter/TypeFilterPresenter.java