bugfix: model str maybe empty (#2660)

api/core/tools/provider/builtin/stablediffusion/tools/stable_diffusion.py

@@ -70,7 +70,7 @@ class StableDiffusionTool(BuiltinTool):
         if not base_url:
             return self.create_text_message('Please input base_url')
 
-        if 'model' in tool_parameters:
+        if 'model' in tool_parameters and tool_parameters['model']:
             self.runtime.credentials['model'] = tool_parameters['model']
 
         model = self.runtime.credentials.get('model', None)