What does your data model look like? If you have a regular Java bean-like object, with fields and getters/setters to define those fields, this isn't easy - GWT doesn't have runtime reflection. The PropertyAccess interface is intended to provide some automatically generated instances for getters and setters, but you have to describe the properties you want access to.
If your data model is a Map<String, ?>, so that you can put arbitrary objects in on the server, and want to read them out with a specific ValueProvider<T,?>, that is pretty easy to do. There are several forum posts that discuss this, as well as a blog post.
Generated PropertyAccess instances can never return null, so such a thing isn't necessary. Or, in this case, legal Java - you can't pass a String (i.e. "None") into the ColumnConfig constructor's first argument (which expects a ValueProvider).
What are you trying to do? Avoid drawing null? Avoid NullPointerExceptions? Can you give a specific example?