Report error if "Next Batch" is clicked before Load Dataset... I could rather disable/enable the button... next life

app.py

@@ -38,7 +38,10 @@ def open_dataset(dataset, subset, split, batch_size, shard, only_rgb, state):
     )
     
 def get_images(batch_size, only_rgb, state):
-    subset = state["subset"]
+    try:
+        subset = state["subset"]
+    except KeyError:
+        raise gr.Error("You need to load a Dataset first")
 
     images = []
     metadatas = []