code: function settings( state = {}, action ) {
  	switch ( action.type ) {
  		case WOOCOMMERCE_MAILCHIMP_SETTINGS_REQUEST_SUCCESS:
  		case WOOCOMMERCE_MAILCHIMP_SETTINGS_REQUEST_FAILURE:
  		case WOOCOMMERCE_MAILCHIMP_API_KEY_SUBMIT_SUCCESS:
  		case WOOCOMMERCE_MAILCHIMP_STORE_INFO_SUBMIT_SUCCESS:
  		case WOOCOMMERCE_MAILCHIMP_CAMPAIGN_DEFAULTS_SUBMIT_SUCCESS:
  		case WOOCOMMERCE_MAILCHIMP_NEWSLETTER_SETTINGS_SUBMIT_SUCCESS:
  			return Object.assign( {}, state, action.settings );
  		case WOOCOMMERCE_MAILCHIMP_LISTS_REQUEST_SUCCESS:
  			const data = { mailchimp_lists: action.lists };
  			const listKeys = keys( action.lists );
  			if ( ! state.mailchimp_list && listKeys.length > 0 ) {
  				// Just pick first that will be shown to the user in the dropdown
  				// We are setting mailchimp_list just in case user likes it and clicks
  				// Continue without actually sellecting something.
  				data.mailchimp_list = listKeys[ 0 ];
  			}
  			return Object.assign( {}, state, data );
  	}
  
  	return state;
  }
docs: Updates state with latest MailChimp connected plugin settings
  
  @param  {Object} state  Current state
  @param  {Object} action Action
  @return {Object}        Updated state