more exception handling

hanlde_form_submit.py

@@ -78,8 +78,13 @@ def on_form_submit(model_name: str, output_length: int, prompt: str) -> str:
         model_name=model_name,
         group_size=output_length,
     )
-    return generate_text(
+    generated_text = generate_text(
         pipeline=pipeline,
         prompt=prompt,
         output_length=output_length,
     )
+    if not isinstance(generated_text, str):
+        raise RuntimeError(f"The model {model_name} did not generate any text.")
+    if len(generated_text) == 0:
+        raise RuntimeError(f"The model {model_name} did not generate any text.")
+    return generated_text