urgent needed

How to get Goods__r.Price__c value it show only empty record

am new to apex

trigger calculate on Item__c (after insert, after update, after delete) {

// Use a map because it doesn't allow duplicate values 
   

Map<ID, Shipping_Invoice__C> updateMap = new Map<ID, Shipping_Invoice__C>();

// Set this integer to -1 if we are deleting 
   
Integer subtract ;

// Populate the list of items based on trigger type 
   
List<Item__c> itemList;
    if(trigger.isInsert || trigger.isUpdate){
        itemList = trigger.new;
        subtract = 1;
    }
    else if(trigger.isDelete)
    {
        // Note -- there is no trigger.new in delete 
   
        itemList = trigger.old;
        subtract = -1;
    }

// Access all the information we need in a single query  
   
// rather than querying when we need it. 
   
// This is a best practice for bulkifying requests 
   

set<Id> AllItems = new set<id>();

for(item__c i :itemList){
// Assert numbers are not negative.   
   
// None of the fields would make sense with a negative value 
   

System.assert(i.quantity__c > 0, 'Quantity must be positive');
System.assert(i.weight__c >= 0, 'Weight must be non-negative');

// If there is a duplicate Id, it won't get added to a set 
   
AllItems.add(i.Shipping_Invoice__C);
}

// Accessing all shipping invoices associated with the items in the trigger 
   
List<Shipping_Invoice__C> AllShippingInvoices = [SELECT id, ShippingDiscount__c,
                   SubTotal__c, TotalWeight__c, Tax__c, GrandTotal__c
                   FROM Shipping_Invoice__C where id in :AllItems];
                  
// Take the list we just populated and put it into a Map.   
   
// This will make it easier to look up a shipping invoice 
   
// because you must iterate a list, but you can use lookup for a map,  
   
Map<ID, Shipping_Invoice__C> SIMap = new Map<ID, Shipping_Invoice__C>();

for(Shipping_Invoice__C sc : AllShippingInvoices)
{
    SIMap.put(sc.id, sc);
}

// Process the list of items 
   
    if(trigger.isUpdate)
    {
        // Treat updates like a removal of the old item and addition of the          
   
        // revised item rather than figuring out the differences of each field  
   
        // and acting accordingly. 
   
        // Note updates have both trigger.new and trigger.old 
   
        for(integer x = 0; x < trigger.old.size(); x++)
        {
            Shipping_Invoice__C myOrder;
            myOrder = SIMap.get(trigger.old[x].Shipping_Invoice__C);

            // Decrement the previous value from the subtotal and weight. 
   
            myOrder.SubTotal__c -= (trigger.old[x].Goods__r.Price__c *
                                    trigger.old[x].quantity__c);
            myOrder.TotalWeight__c -= (trigger.old[x].weight__c *
                                       trigger.old[x].quantity__c);
               
            // Increment the new subtotal and weight. 
   
            myOrder.SubTotal__c += (trigger.new[x].Goods__r.Price__c *
                                    trigger.new[x].quantity__c);
            myOrder.TotalWeight__c += (trigger.new[x].weight__c *
                                       trigger.new[x].quantity__c);
        }
       
        for(Shipping_Invoice__C myOrder : AllShippingInvoices)
        {
           
            // Set tax rate to 9.25%  Please note, this is a simple example.   
   
            // Generally, you would never hard code values. 
   
            // Leveraging Custom Settings for tax rates is a best practice.   
   
            // See Custom Settings in the Apex Developer's guide  
   
            // for more information. 
   
            myOrder.Tax__c = myOrder.Subtotal__c * .0925;
           
            // Reset the shipping discount 
   
            myOrder.ShippingDiscount__c = 0;
   
            // Set shipping rate to 75 cents per pound.   
   
            // Generally, you would never hard code values. 
   
            // Leveraging Custom Settings for the shipping rate is a best practice. 
   
            // See Custom Settings in the Apex Developer's guide  
   
            // for more information. 
   
            myOrder.Shipping__c = (myOrder.totalWeight__c * .75);
            myOrder.GrandTotal__c = myOrder.SubTotal__c + myOrder.tax__c +
                                    myOrder.Shipping__c;
            updateMap.put(myOrder.id, myOrder);
         }
    }
    else
    {
        for(Item__c itemToProcess : itemList)
        {
            Shipping_Invoice__C myOrder;
   
            // Look up the correct shipping invoice from the ones we got earlier 
   
            myOrder = SIMap.get(itemToProcess.Shipping_Invoice__C);
            if(itemToProcess.Goods__r.Price__c != null){
            myOrder.SubTotal__c += (itemToProcess.Goods__r.Price__c *
                                   itemToProcess.quantity__c * subtract);
            }
            myOrder.TotalWeight__c += (itemToProcess.weight__c *
                                       itemToProcess.quantity__c * subtract);
        }
       
        for(Shipping_Invoice__C myOrder : AllShippingInvoices)
        {
           
             // Set tax rate to 9.25%  Please note, this is a simple example.   
   
             // Generally, you would never hard code values. 
   
             // Leveraging Custom Settings for tax rates is a best practice.   
   
             // See Custom Settings in the Apex Developer's guide  
   
             // for more information. 
   
             myOrder.Tax__c = myOrder.Subtotal__c * .0925;
            
             // Reset shipping discount 
   
             myOrder.ShippingDiscount__c = 0;
   
            // Set shipping rate to 75 cents per pound.   
   
            // Generally, you would never hard code values. 
   
            // Leveraging Custom Settings for the shipping rate is a best practice. 
   
            // See Custom Settings in the Apex Developer's guide  
   
            // for more information. 
   
            myOrder.Shipping__c = (myOrder.totalWeight__c * .75);
            myOrder.GrandTotal__c = myOrder.SubTotal__c + myOrder.tax__c +
                                    myOrder.Shipping__c;
                                      
            updateMap.put(myOrder.id, myOrder);
   
         }
     }   
    
     // Only use one DML update at the end. 
   
     // This minimizes the number of DML requests generated from this trigger. 
   
     update updateMap.values();
}