code: protected function getDefaultFacets() {
  		$availableFacets = $this->getAvailableFacets();
  		return array_combine(array_keys($availableFacets), array_fill(0, count($availableFacets), array()));
  	}
docs: Returns an array of preselected facets (no facet selected is the default)
  
  @return string[string][]