I'm very new to Conversation, and have had a similar problem working with entities, but I believe the same would work for intents.
When getting car make and model, I have two entities @makes and @models.
In the Dialog, after asking for Make and Model, I have nodes for:
@makes and @models - This means they have matched the values in both Entities.
@makes and not(@models) - This means they have matched only Makes.
not(@makes) and @models - This means they have matched only Models.
not(@makes) and not(@models) - This means they haven't matched either of the entities.
Depending on which node they hit, you can branch off to an appropriate node.
For the "not(@xxxxxx)" condition, you have to type it in full on the "Enter a condition" line, it won't pre-populate the dropdown lists.