_createStyleIfNeeded() {
        if (!this._style) {
            const styleId = this._node.attributes.s;
            this._style = this.workbook().styleSheet().createStyle(styleId);
            this._node.attributes.s = this._style.id();
            this._node.attributes.customFormat = 1;
        }
    }
Create a style for this row if it doesn't already exist.
@returns {undefined}
@private