No selection option wanted in ComboBox with ComboBoxAttachment

I am using the ComboBoxAttachment to save my combobox selection which is working great except that I cannot get the combobox be empty.
Before creating the valurtree attachment this could be done by setting comboBox.setSelectedId(0) but now that the attachment has been set the values seem to be restricted to them and attempting to select nothing makes the comboboxs first item appear instead.

This line from the documentation suggests to me there’s no option for an empty combobox, is that right? Is there another way to empty the combobox?

Combobox items will be spaced linearly across the range of the parameter. For example if the range is specified by NormalisableRange (-0.5f, 0.5f, 0.5f) and you add three items then the first will be mapped to a value of -0.5, the second to 0, and the third to 0.5.