Yes, if not slot_values: means that your user didn’t provide the requested information so the value of slot_to_fill ( slot_to_fill or the value of requested_slot slot) is None.
When the user doesn’t provide the requested information, an ActionExecutionRejection will raise and rasa will try to predict another action but this form remains active and the value of requested_slot slot remains the same. Rasa continues its path but It always waits for the value of requested_slot to finish the form and deactivate it. Until that time you can not activate another form.
I want to be able to deactivate the form. I don’t want to get the value of requested_slot slot form user anymore. So, I tried to deactivate this form by tracker.active_form = {} and tell rasa to move on and stop waiting for the value of tracker.slots["requested_slot"]. But this is not the right way to achieve this goal.