ExtJS: Problem with Grid rowExpander plugin (collapseAll doesn't work)

    // A row expander for newsletter grid rows (additional informations)
    this.exp = new Ext.ux.grid.RowExpander({
        tpl: new Ext.Template(nlInfos)
        ,enableCaching: false
    });

    {
            xtype: 'xcheckbox'
            ,id: 'autorefresh'
            ,name: 'autorefresh'
            ,boxLabel: _('goodnews.newsletter_grid_autorefresh')
            ,description: _('goodnews.newsletter_grid_autorefresh_tooltip')
            ,hideLabel: true
            ,ctCls: 'gon-checkbox-toggle'
            ,inputValue: 1
            ,listeners: {
                'check': function(cbx,checked){
                    this.collapseAll();
                    this.toggleAutoRefresh(cbx,checked);
                }
                ,scope:this
            }
        }

Uncaught TypeError: this.exp.collapseAll is not a function
    at GoodNews.grid.Newsletters.collapseAll (modx.grid.js:512)
    at GoodNews.grid.Newsletters.check (newsletters.panel.js:270)
    at h.Event.fire (ext-all.js:21)
    at S.fireEvent (ext-all.js:21)
    at S.setValue (ext-all.js:21)
    at S.setValue (utilities.js:509)
    at S.onClick (ext-all.js:21)
    at HTMLInputElement.I (ext-all.js:21)

    ,collapseAll: function() {
        if (!this.exp) return false;

        this.exp.collapseAll(); <--- this line throws an error!
        this.tools['minus'].hide();
        this.tools['plus'].show();
        return true;
    }