Fix: Resolve type mismatch in PhotoReasoningViewModel.reason() for imageUris.

Corrected a build error caused by a type mismatch when creating a
PhotoReasoningMessage within the `reason` method. The `imageUrisForChat`
parameter (List<String>?) was being assigned to the `imageUris` field,
which expected a non-nullable List<String>.

The fix uses the Elvis operator to provide `emptyList()` if
`imageUrisForChat` is null:
`imageUris = imageUrisForChat ?: emptyList()`

This ensures a non-nullable list is always passed, resolving the
compilation error and maintaining the intended logic for displaying
images in chat messages.

Author: google-labs-jules[bot]

app/src/main/kotlin/com/google/ai/sample/feature/multimodal/PhotoReasoningViewModel.kt

@@ -137,7 +137,7 @@ class PhotoReasoningViewModel(
         val userMessage = PhotoReasoningMessage(
             text = aiPromptText, // Use the combined text
             participant = PhotoParticipant.USER,
-            imageUris = imageUrisForChat, // Use the new parameter here
+            imageUris = imageUrisForChat ?: emptyList(), // Use the new parameter here
             isPending = false
         )
         _chatState.addMessage(userMessage)