Set the height of an item inside a JCombobox

I have a JCombobox with many items and first of all them is a NULL value

When opening the combobox, all the items have a normal height but not the first one which is a really thin strip at the top of all. That makes really difficult to be clickable since it looks like the开发者_如何学运维re is nothing (but it is there and you can select it).

The question is, how can I make this item to have the same height than the other items?

More information:

• I have tried with JCombobox.setPrototypeDisplayValue() with a normal String like "XXXXX" or with one of the normal items, but that changes the width but not the height.
• The null value is represented in the JCombobox with an empty String ("") via a ObjectToStringConverter subclass:

org.jdesktop.swingx.autocomplete.AutoCompleteDecorator.decorate (combobox, ConfigurableToStringConverter.INSTANCE);

Thanks in advance

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Override the default renderer used for comboboxes (see DefaultListCellRenderer class). Check the getListCellRendererComponent() method. Call super.getListCellRendererComponent() and if value is NULL set empty string (or space char string " ") as the value.

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Looking at camickr's Combo Box Popup, the code source shows setPreferredSize for Width, but I can't see any reason not to use setPreferredSize for Height the same way.

There is only question is if there may be some conflict between SwingX#AutoCompleteDecorator and standard Swing code