ClassCastException when not filling the second parameter on an integer between filter (tryed with 'id')

Plan to reproduce:

Preparation:
Simply add a filterpane as described on the plugin page on a scaffolded app.
Additional add the id parameter.

Steps:

• Open the filterpane and select 'between' on the id.
• Fill the first parameter with a correct value (any number).
• Dont fill the second parameter.

• Execute the filter.

Result:
java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Long

On other wrong input it does a good job but there it results in a RunTimeExeption.

Some general Idea:

For sure it would be nice, if there was some warnings on bad inputs.
Maybe in a way it happens with the wrong input on scaffolded grails-forms.

Possibly with a tag like the currentCriteria criteria tag, or directly in the form.
Anyways this are just ideas, while the bug remains.

Hope that helps you improve that awesome Plugin you devoloped.