Error training Dialogue Manager

Hello everyone, I'm failing to train my dialogue mgmt model. Please assist.

the error is

slot_class = Slot.resolve_by_type(slot_dict[slot_name].get("type"))
AttributeError: 'NoneType' object has no attribute 'get'

Here is the sample code that stores a student name

class ActionName(Action):
    def name(self):
        return "action_student_name"

    def run(self, dispatcher, tracker, domain):
        name = tracker.get_slot('student_name')
        student_name = next(tracker.get_latest_entity_values('name'), None)

        if not student_name:
            student_name = tracker.latest_message.get('text')

        return [SlotSet('student_name', student_name)]

from the error it seems that the input scentence that is triggring your action ‘action_student_name’ ,from that sentence the NLU is able to find the intent correctly but it is not able to find the entity ‘student_name’ in that sentence.