public DocRef getSelectedEntityReference() {
        return value;
    }
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