clarify failure

app.py

@@ -101,7 +101,7 @@ def infer(code):
 
     field_prompt_result, fields, field_helper_result = field_prompt(code)
     if len(fields) == 0:
-        field_output = "No fields"
+        field_output = "Failed to parse fields" if field_prompt_result is None else "No fields"
     else:
         field_input_ids = tokenizer.encode(field_prompt_result, return_tensors="pt").cuda()[
             :, : 8192 - 1024