BUG - Missing fields on custom locations cause json errors

[mak001]

Describe the bug
When using a custom object as a location if Featured is not a field on the object the json endpoint generates invalid json.

To Reproduce
Steps to reproduce the behavior:

1. Create a custom location object without a Featured field
2. Set locator to use new class as location
3. run a dev/build?flush=all
4. visit the locator page and add the json action

Expected behavior
Valid json is generated

This is what is generated currently without a Featured field of getter

{
   "locations":[
      {
         "ID":1,
         "Title":"#1",
         "Featured":,
         "Website":"",
         "Phone":"",
         "Fax":"",
         "Email":"",
         "Address":"",
         "Address2":"",
         "City":"Sheboygan",
         "State":"WI",
         "PostalCode":"53081",
         "Country":"us",
         "Distance":-1,
         "Lat":43.7013054,
         "Lng":-87.7271123
      }
   ]
}

Possible solutions
Make data templates try to find location object specific templates. Possibly add fall back support to a basic template with bare minimum field requirements.

The fix should also be implemented to the XML feed to keep everything consistent.