Error onColumnShow in a grouped header grid

[wqjh7809]

In my grid I'm using a grouped header like this:

{ text: arrMonths[0]["name"],
    id: 'monthCol0',
    sortable: false,
    groupable: false,
    columns: [{
        text: 'Quantity',
        dataIndex: 'Quantity0', 
        id: 'QuantCol0', 
        width: 50, 
        renderer: formatEuropeanZeroDecimal, 
        hidden: true, 
        align: 'right', 
        sortable: false, 
        groupable: false,
            editor: getNumberFieldEditor()
                },{
        text: 'Value', 
        dataIndex: 'Value0', 
        width: 75, 
        renderer: formatEuropeanTwoDecimal, 
        align: 'right', 
        sortable: false, 
        groupable: false,
        editor: getNumberFieldEditor()
    }]
}

 function getNumberFieldEditor(nf) {
            return new Ext.form.field.Number({
                xtype: 'numberfield',
                minValue: 0,
                hideTrigger: true,
                decimalSeparator: ',',
                listeners: {
                    focus: function (nf) {                    
                    //...    
                    },
                    blur: function () {
                    //...
                    }
                }
            });
        }

When I'm clicked in the header menu to hide the whole grouped column and then to show them again, I get the following error:

The object does not support the property or method "GetEditor"

in this section of Ext:

Ext.define('Ext.grid.RowEditor', {
    extend: 'Ext.form.Panel',
    requires: [
        'Ext.tip.ToolTip',
        'Ext.util.HashMap',
        'Ext.util.KeyNav'
    ],

//(...)

    onColumnShow: function(column) {
        var field = column.getEditor(); <==

//(...)

In this context

column

is the grouped column, without an editor.

What's wrong in the code?

[wqjh7809]

Is fixed in 4.1.3.