The campingList JavaScript controller isn't calling 'saveItem'

The Trailhead challenge check is telling me the following:

Challenge Not yet complete… here’s what’s wrong:
The campingList JavaScript controller isn’t calling ‘saveItem’ in the Apex class to save the record or setting the ‘item’ as a parameter for the ‘saveItem’ action.

The app is really not working as expected, but I can not guess why is that.

Here is my code.

campingApp.app :

<aura:application extends="force:slds">
    <c:camping />
</aura:application>

camping.cmp :

<aura:component controller="CampingListController">
    <aura:handler name="init" action="{!c.doInit}" value="{!this}"/>
    <aura:attribute name="items" type="Camping_Item__c[]" default="[]"/>
    <aura:attribute name="item" type="Camping_Item__c" default="{ 
                        'sobjectType': 'Camping_Item__c',
                        'campingItemName': 'campingItemNameDefault',
                        'Price__c': 0,
                        'Quantity__c': '0',
                        'Packed__c': false }"/>
    <c:campingHeader />
    <!-- <c:campingItemForm item="{!v.item}" items="{!v.items}" /> -->
    <c:campingList items="{!v.items}"/>
</aura:component>

CampingListController.apxc :

public class CampingListController {
    @AuraEnabled
    public static List<Camping_Item__c> getItems() {
        return [SELECT Id, Name, Quantity__c, Price__c, Packed__c FROM Camping_Item__c];
    }

    @AuraEnabled
    public static Camping_Item__c saveItem(Camping_Item__c item) {
        upsert item;
        return item;
    }
}

campingController.js :

({
    logArray : function(component, event, helper) {
        var items = component.get("v.items");
        console.log(JSON.stringify(items));
    },
    doInit: function(component, event, helper) {
        var action = component.get("c.getItems");
        action.setCallback(this, function(response) {
            var state = response.getState();
            if (state === "SUCCESS") {
                component.set("v.items", response.getReturnValue());
            }
            else {
                console.log("Failed with state: " + state);
            }
        });
        $A.enqueueAction(action);
    }
})

campingHeader.cmp :

<aura:component >
<lightning:layout class="slds-page-header slds-page-header--object-home">
        <lightning:layoutItem >
            <lightning:icon iconName="action:goal"/>
        </lightning:layoutItem>
        <lightning:layoutItem padding="horizontal-small">
            <div class="page-section page-header">
                <h1 class="slds-text-heading--label">Camping list</h1>
            </div>
        </lightning:layoutItem>
    </lightning:layout>

</aura:component>

campingList.cmp :

<aura:component controller="CampingListController">
    <aura:attribute name="items" type="Camping_Item__c[]" />
    <aura:handler name="addItemEvent" event="c:addItemEvent"
        action="{!c.handleAddItem}"/>
    <c:campingListForm/>
    <aura:iteration items="{!v.items}" var="item">
        <c:campingListItem item="{!item}" />
    </aura:iteration>

</aura:component>

campingListController.js :

({
    clickCreateItem : function(component, event, helper) {
        var isValidItem = component.find('campingItemForm').reduce(function(total,currentValue, index,arr)
                                                           {
                                                               currentValue.showHelpMessageIfInvalid();
                                                               return total && currentValue.get('v.validity').valid;
                                                           }, true);
        if(isValidItem) {
            helper.createItem(component);
        }
    },
    doInit: function(component, event, helper) {
        var action = component.get("c.getItems");
        action.setCallback(this, function(response) {
            var state = response.getState();
            if (state === "SUCCESS") {
                component.set("v.items", response.getReturnValue());
            }
            else {
                console.log("Failed with state: " + state);
            }
        });
        $A.enqueueAction(action);
    },
    handleAddItem: function(component, event, helper) {
        var item = event.getParam("item");
        helper.updateExpense(component, item);
    }
})

campingListHelper.js :

({
    createItem : function(component, item) {
        var action = component.get("c.saveItem");

            //var newItem = component.get("v.newItem");
            action.setParams({
                "item": item
            });

            action.setCallback(this, function(response){
                var state = response.getState();
                if (state === "SUCCESS") {
                    var items = component.get("v.items");
                    items.push(response.getReturnValue());
                    item = {sobjectType: "Camping_Item__c"};;
                    component.set("v.newItem", item);
                    component.set("v.items", items);
                }
            });

            $A.enqueueAction(action);
    }
})

campingListForm.cmp :

<aura:component controller="CampingListController">
    <aura:attribute name="newItem" type="Camping_Item__c" default="{ 
                        'sobjectType': 'Camping_Item__c',
                        'campingItemName': 'SSSSSSSSSSSSSSSSS',
                        'Price__c': 0,
                        'Quantity__c': '0',
                        'Packed__c': false }"/>
    <aura:registerEvent name="addItem" type="c:addItemEvent"/>
    <form class="slds-form--stacked">      
            <lightning:input aura:id="campingItemForm" label="Name"
                             name="Name"
                             value="{!v.newItem.Name}"/>
            <lightning:input type="number" aura:id="campingItemForm" label="Quantity"
                             name="Quantity"
                             min="1"
                             step="1"
                             value="{!v.newItem.Quantity__c}"
                             placeholder="0"/>
            <lightning:input type="number" aura:id="campingItemForm" label="Price"
                             name="Price"
                             formatter="currency"
                             value="{!v.newItem.Price__c}"/>
            <lightning:input aura:id="campingItemForm" type="checkbox" label="Packed"  
                             name="campingItemIsPacked"
                             checked="{!v.newItem.Packed__c}"/>
            <lightning:button label="Create Camping Item" 
                              class="slds-m-top--medium"
                              variant="brand"
                              onclick="{!c.clickCreateItem}"/>
        </form>
</aura:component>

campingListFormController.js :

({
    clickCreateItem : function(component, event, helper) {
        var isValidItem = component.find('campingItemForm').reduce(function(total,currentValue, index,arr)
                                                           {
                                                               currentValue.showHelpMessageIfInvalid();
                                                               return total && currentValue.get('v.validity').valid;
                                                           }, true);
        if(isValidItem) {
            helper.createItem(component);
        }
    }
})

campingListHelper.js :

({
    createItem : function(component) {
        var action = component.get("c.saveItem");

            var newItem = component.get("v.newItem");
            action.setParams({
                "item": newItem
            });

            action.setCallback(this, function(response){
                var state = response.getState();
                if (state === "SUCCESS") {
                    /* var items = component.get("v.items");
                    items.push(response.getReturnValue());
                    newItem = {sobjectType: "Camping_Item__c"};
                    component.set("v.newItem", newItem);
                    component.set("v.items", items); */

                    var addItemEvent = component.getEvent("addItem");
                    addItemEvent.setParams({"item": response.getReturnValue()});
                    addItemEvent.fire();
                    newItem = {sobjectType: "Camping_Item__c"};
                    component.set("v.newItem", newItem);
                }
            });

            $A.enqueueAction(action);
    }
})

addItemEvent.evt :

<aura:event type="COMPONENT">
    <aura:attribute name="item" type="Camping_Item__c"/>
</aura:event>

As you can tell from the line :

<aura:component controller="CampingListController">

in the campingList.cmp the .apxc controller is attached to the campingList.cmp.

Next, as you can tell from the line :

helper.updateExpense(component, item);

in the campingListController.js and then from the line :

var action = component.get("c.saveItem");

in the campingListHelper.js the .apxc function saveItem is called.

So, what is still needs to be checked is that the event arrives to the handler in campingList.cmp.

Here is the event which will be thrown from the campingListForm.cmp :

<aura:registerEvent name="addItem" type="c:addItemEvent"/>

and in the campingListFormHelper.js it is actually thrown :

addItemEvent.fire();

Hence I am expecting the even to get caught in the campingList.cmp over here:

<aura:handler name="addItemEvent" event="c:addItemEvent"
        action="{!c.handleAddItem}"/>

and as a result call the saveItem function.

But the Trailhead continues to tell me that that call does not happen. And after debugging I see that it really does not. What am I doing wrong here?

<aura:registerEvent name="addItem" type="c:addItemEvent"/>
<aura:handler name="addItemEvent" event="c:addItemEvent"
        action="{!c.handleAddItem}"/>

<aura:registerEvent name="addItem" type="c:addItemEvent"/>
<aura:handler name="addItem" event="c:addItemEvent"
        action="{!c.handleAddItem}"/>

handleAddItem: function(component, event, helper) {
    var item = event.getParam("item");
    helper.updateExpense(component, item);
}