Gradio Textbox - None type as input

Question

I'm working on a recommender system that uses gradio interface for text input. When asking for bag of words suggestions, bow_input is seen as "string" => fine

When asking for Bert suggestions, bert input is seen as none. Here are the logs :

text input None
WARNING:root:Received None as text input

Here's the code of Gradio interface :

def setup_gradio_interface():
       with gr.Blocks() as recommander:
            with gr.Tab("Bag of words suggestions"):
               bow_input = gr.Textbox(label="Tell me what you want...")
               bow_output = gr.Textbox(label="I tell you what to watch!")
               bow_button = gr.Button("Generate your top 5 BOW recos.")
               bow_button.click(process_BOW, inputs=bow_input, outputs = bow_output) 
            pass
      with gr.Tab("BERT suggestions"):
            bert_input = gr.Textbox(label="Tell me what you want...")
            bert_output = gr.Textbox(label="I tell you what to watch!")
            bert_button = gr.Button("Generate your top 5 BERT recos.")
            bert_button.click(process_BERT, inputs=bert_input, outputs=bert_output)
   return recommander

here is the beginning of my pipeline to create embeddings and send request to Flask:

def process_BERT (bertmodel, bert_input):
    print("text input",bert_input)
    embedding_BERT = create_bert_embeddings(bertmodel,bert_input)

that calls

def create_bert_embeddings(tokenizer, text_input):
    if text_input is None:
        logging.warning("Received None as text input")
        return None
    print("text_input type:", type(text_input))
    text_input=str(text_input)
    input=clean_text(text_input)

Any idea why is the input "None"?

I tried to debug with logging, share common interface between BOW and Bert input, and try on an isolate app for Bert. Still the same problem.