I can think on 2 ways to do this.
first one, the search souled be with no mandatory fields, by search RequestFilter you will check if there is at least 1 property value but check the json search criteria values, if all are empty, you can return an error msg dialog.
the other way is to use PropertyEditor you can find info on the redbook and samplePropertyEditor files. (can also add msg on one field, or change his HTML + js).
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