Undefined method ViewsEFFieldsetData::tree_to_fapi()

views_ef_fieldset.module makes reference to a tree_to_fapi() function in ViewsEFFieldsetData:

$form['filters']['children'] = $viewsEFFieldsetData->tree_to_fapi();

This function doesn't exist. There is a ViewsEFFieldsetData::treetofapi() function, without the hyphens:

public function treetofapi() {