How to add an empty item to ExtJS combobox?

Question

I want to add and empty item (display value is blank, item height is kept as normal) to an Ext.form.ComboBox. I refered 2 links below to configure my combobox, but it still

Answer 1

In Ext 4.2.1 (probably others), just add to combobox config:

tpl : '
{fullName} '