Update nil Ref check and property decode warning to new Rojo protocol (#466)

* Skip empty Refs in new Rojo protocol

* Update warning message for new Rojo protocol

plugin/src/Reconciler/diff.lua

@@ -75,7 +75,9 @@ local function diff(instanceMap, virtualInstances, rootId)
 						changedProperties[propertyName] = virtualValue
 					end
 				else
-					Log.warn("Failed to decode property of type {}", virtualValue.Type)
+					-- virtualValue can be empty in certain cases, and this may print out nil to the user.
+					local propertyType = next(virtualValue)
+					Log.warn("Failed to decode property of type {}", propertyType)
 				end
 			else
 				local err = existingValueOrErr