You can check if a property exists by using the hasPath() method. In this example, the previous snap only passed an element called, fileDate. The element, noSuchProperty, was not passed into the snap.
Alternatively, depending on what you ultimately want to achieve, you might also want to use the get() method. This method will check to see if your element exists. If it does, then the element will be evaluated and its value will be passed into your target path. If it does not exist, then a null value will be passed into your target path.
Using these suggestions might fit into the constraints of the Data Validator snap, but I think it would give you what you’re looking for.
