Please refer to the very simple testcase attached.
I only want the fields displayed in the Multibox that contain a value.
1. Select Fred. There are 2 Freds in Los Angeles with different zip codes. I don't want the Zip field to show up in the Multibox
2. Select Mary. There are 2 Marys with different cities and different zip codes. I only want to see the Name field in the Multibox