framework/grid/DataColumn.php
protected function renderHeaderCellContent()
    {
        if ($this->header !== null || $this->label === null && $this->attribute === null) {
            return parent::renderHeaderCellContent();
        }

        $label = $this->getHeaderCellLabel();
        if ($this->encodeLabel) {
            $label = Html::encode($label);
        }

        if ($this->attribute !== null && $this->enableSorting &&
            ($sort = $this->grid->dataProvider->getSort()) !== false && $sort->hasAttribute($this->attribute)) {
            return $sort->link($this->attribute, array_merge($this->sortLinkOptions, ['label' => $label]));
        }

        return $label;
    }
protected function renderHeaderCellContent()
    {
        if ($this->header !== null || $this->label === null && $this->attribute === null) {
            return parent::renderHeaderCellContent();
        }

        $label = $this->getHeaderCellLabel();
        if ($this->encodeLabel) {
            $label = Html::encode($label);
        }

        if ($this->attribute !== null && $this->enableSorting &&
            ($sort = $this->grid->dataProvider->getSort()) !== false && $sort->hasAttribute($this->attribute)) {
            return $sort->link($this->attribute, array_merge($this->sortLinkOptions, ['label' => $label]));
        }

        return $label;
    }
{@inheritdoc}