[Bug?] when adding table items to a rollable table?

Whenever I create items for a rollable table I get this warning? "ERROR: You cannot set the imgsrc or avatar of an object unless you use an image that is in your Roll20 Library. See the API documentation for more info." I'm not supplying an avatar in my createObj() call and letting it default to "". Should I be doing something else? Here's the call: var newItem = createObj('tableitem',{ _rollabletableid: newTable.id, name: r, weight: weight });