I am using redux and I have a state with empty string values. Each empty key has to be filled in using input onChange event. Say I want to change 'business\_selected' key, what should the function look like? Here's my state: 

```

const initialState = {

        user: {},
        applications: [
            {
                companyFlow: {
                    stage1: {
                        business_activity: "",
                        business_selected: ""
                    },

                    stage2: {
                        legal_name: "",
                        registration_number: "",
                        business_website: "",
                        incorporation_date_text: "",
                        legal_form: ""
                    }
                }
            }
        ]
};

export default function changeInput(state = initialState, action) {
  switch (action.type) {
    case CHANGE_INPUT:
      return {
        // ??????
      };
    default:
      return state;
  }
}

```