why doesn't response_mime_type = json work here?

[fredzanarbor]

class init:

self.generation_config = {
"temperature": 1,
"top_p": 0.95,
"top_k": 0,
"max_output_tokens": 8192,
}

def process_text(self, model_name, safety_settings, generation_config, text, system_instruction, user_prompt):

    self.configure_api()
    try:
        model = genai.GenerativeModel(model_name, safety_settings, generation_config)
    except Exception as e:
        logging.error(f"error creating model {e}")
        print(f"error creating model {e}")
    prompt = [system_instruction, user_prompt, text]

    try:
        response = model.generate_content(prompt, generation_config={'response_mime_type':'application/json'})
    except Exception as e:
        logging.error(f"error generating content {e}")
        print(f"error generating content {e}")
    print(response)

more code:

def create_model(self, model_name, safety_settings, generation_config, system_instruction):
    model = genai.GenerativeModel(model_name, safety_settings, generation_config, system_instruction)
    return model

Traceback (most recent call last):
File "/Users/fred/bin/nimble/bookpublisherGPT/classes/SyntheticReaders/gemini2syntheticreaders/text2gemini.py", line 91, in <module>
t2g.process_text(t2g.model_name, t2g.safety_settings, t2g.generation_config, text, t2g.system_instruction,
File "/Users/fred/bin/nimble/bookpublisherGPT/classes/SyntheticReaders/gemini2syntheticreaders/text2gemini.py", line 72, in process_text
print(response)
UnboundLocalError: local variable 'response' referenced before assignme