public function makeFilter(
        $filterType = null,
        $filterField = null,
        $filterValue = null
    ) {
        if ($filterType === null &&
            $filterField === null &&
            $filterValue === null)
            $this->filter = array();
        else
            $this->filter = array(
                'filter_type' => $filterType,
                'filter_field' => $filterField,
                'filter_value' => $filterValue
            );

        return $this;
    }