private function addSortFields(Fieldset $fieldset)
    {
        $sortFieldsOptions = [
            ['value' => '_first', 'label' => __("First")],
            ['value' => '_last',  'label' => __("Last")],
        ];

        $fieldset->addField(
            'sort_order_asc_missing',
            'select',
            [
                'name'   => 'sort_order_asc_missing',
                'label'  => __('Sort products without value when sorting ASC'),
                'values' => $sortFieldsOptions,
                'note'   => __('How the products which are missing values for this attribute should be treated when using it to sort.'),
            ],
            'used_for_sortby'
        );

        $fieldset->addField(
            'sort_order_desc_missing',
            'select',
            [
                'name'   => 'sort_order_desc_missing',
                'label'  => __('Sort products without value when sorting DESC'),
                'values' => $sortFieldsOptions,
                'note'   => __('How the products which are missing values for this attribute should be treated when using it to sort.'),
            ],
            'sort_order_asc_missing'
        );

        return $this;
    }
private function addSortFields(Fieldset $fieldset)
    {
        $sortFieldsOptions = [
            ['value' => '_first', 'label' => __("First")],
            ['value' => '_last',  'label' => __("Last")],
        ];

        $fieldset->addField(
            'sort_order_asc_missing',
            'select',
            [
                'name'   => 'sort_order_asc_missing',
                'label'  => __('Sort products without value when sorting ASC'),
                'values' => $sortFieldsOptions,
                'note'   => __('How the products which are missing values for this attribute should be treated when using it to sort.'),
            ],
            'used_for_sortby'
        );

        $fieldset->addField(
            'sort_order_desc_missing',
            'select',
            [
                'name'   => 'sort_order_desc_missing',
                'label'  => __('Sort products without value when sorting DESC'),
                'values' => $sortFieldsOptions,
                'note'   => __('How the products which are missing values for this attribute should be treated when using it to sort.'),
            ],
            'sort_order_asc_missing'
        );

        return $this;
    }
private function addSortFields ( Fieldset $ fieldset ) { $ sortFieldsOptions = [ [ 'value' => '_first' , 'label' => __ ( "First" ) ] , [ 'value' => '_last' , 'label' => __ ( "Last" ) ] , ] ; $ fieldset -> addField ( 'sort_order_asc_missing' , 'select' , [ 'name' => 'sort_order_asc_missing' , 'label' => __ ( 'Sort products without value when sorting ASC' ) , 'values' => $ sortFieldsOptions , 'note' => __ ( 'How the products which are missing values for this attribute should be treated when using it to sort.' ) , ] , 'used_for_sortby' ) ; $ fieldset -> addField ( 'sort_order_desc_missing' , 'select' , [ 'name' => 'sort_order_desc_missing' , 'label' => __ ( 'Sort products without value when sorting DESC' ) , 'values' => $ sortFieldsOptions , 'note' => __ ( 'How the products which are missing values for this attribute should be treated when using it to sort.' ) , ] , 'sort_order_asc_missing' ) ; return $ this ; }
Append sorting related fields.

@param Fieldset $fieldset Target fieldset

@return FrontPlugin
Append sorting related fields .