public function getIndexHeaderCells(array $fields = null)
    {
        $stub = $this->getStubContent('index.header.cell.blade', $this->template);
        $fields = $this->getFieldsToDisplay($fields);
        $rows = '';

        foreach ($fields as $field) {
            if ($field->isOnIndexView) {
                $row = $stub;
                $this->replaceFieldTitle($row, $this->getTitle($field->getLabel(), true))
                    ->replaceCommonTemplates($row, $field);
                $rows .= $row . PHP_EOL;
            }
        }

        return $rows;
    }