I use the INSearchForNotebookItemsIntent to display lists and items in Siri's interface with a custom Intent UI. When returning a successful INSearchForNotebookItemsIntentResponse with only a single task list in the TaskLists array property and (and the tasks array of the response empty), SiriKit fails to load my custom Intents UI and instead loads Apple's default one.
If multiple multiple task lists are supplied, the custom Intents UI is loaded as expected.
What is even worse is that Apple's UI has these weird checkboxes that neither coordinate with my app or the custom Intent UI nor do anything. They're not wired anywhere and even though they look identical to Apple's Reminder's checkboxes, tapping them does nothing and there's no way to provide interaction.
To get around this, I've been stuffing a dummy INTask object into the tasks array on the response, which causes the the Custom UI to render (discovered this trick from the Things app's Siri interface) but would really really like to not do this: It adds a residual "header" at the bottom of the custom UI that says Items and when Siri speaks, she'll say something along the lines of "Two items were found" since the dummy is being considered alongside the found list.
I've learned YMMV with the SiriKit API since I started working with it, but this is a particular issue that plagues my app and continues to exist into the iOS 12 previews.
