Update app.py

app.py

@@ -17,7 +17,8 @@ def read_content(file_path: str) -> str:
     return content
 
 def predict(dict, prompt="", negative_prompt="", guidance_scale=7.5, steps=20, strength=1.0, scheduler="EulerDiscreteScheduler"):
-
+    if negative_prompt == "":
+        negative_prompt = None
     scheduler_class_name = scheduler.split("-")[0]
 
     add_kwargs = {}