public void setTags(final Collection<String> tags) {
        explorerPopupPresenter.setTags(NullSafe.stream(tags)
                .toArray(String[]::new));
    }
Call this if the selection box contains more than one {@link DocRef} type,
e.g. all data source types. Value should be singular and in
sentence case, e.g. 'Data Source'.

@param itemType
stroom-core-client/src/main/java/stroom/explorer/client/presenter/DocSelectionBoxPresenter.java