ExtJS: How can I set a specific CSS class for a grid row?

Ext.applyIf(config,{
    id: 'goodnews-grid-subscribers'
    ,url: GoodNews.config.connectorUrl
    ,baseParams: { action: 'mgr/subscribers/getList' }
    ,viewConfig: {
        getRowClass: function(record,rowIndex,rowParams,store) {
            return (record.get('grpcount') == 0) ? 'gon-no-subscriptions' : '';
        }
    }
    ...

Ext.applyIf(config,{
    id: 'goodnews-grid-subscribers'
    ,url: GoodNews.config.connectorUrl
    ,baseParams: { action: 'mgr/subscribers/getList' }
    ,getRowClass: function(record,rowIndex,rowParams,store) {
        return (record.get('grpcount') == 0) ? 'gon-no-subscriptions' : '';
    }
    ...

        
        id: 'goodnews-grid-subscribers'
        ,url: GoodNews.config.connectorUrl
        ,baseParams: { action: 'mgr/subscribers/getList' }
        ,fields: [
            'id'
            ,'username'
            ,'fullname'
            ,'email'
            ,'testdummy'
            ,'active'
            ,'createdon_formatted'
            ,'ip'
            ,'soft_bounces'
            ,'hard_bounces'
            ,'grpcount'
            ,'menu'
        ]
        ,emptyText: _('goodnews.subscribers_none')
        ,paging: true
        ,remoteSort: true
        ,viewConfig: {
            forceFit: true
            ,enableRowBody: true
            ,scrollOffset: 0
            ,autoFill: true
            ,showPreview: true
            ,getRowClass: function (record,index,rowParams,store) {
                if (record.get('grpcount') == 0) {
                    return 'gon-no-subscriptions-gridrow';
                } else {
                    return '';
                }
            }
        }
        ,plugins: [this.subexpander]
        ,autoExpandColumn: 'username'
        ,columns: [
        ...