Please provide steps and a simple example with apex code

Attempt to de-reference a null object - Need Help with Trigger

Hi, 
I need help with a trigger. Someone please help me on what I am doing wrong. Thank you.
My scenario is - For a person Account - Address, City & Zip are filled.
When a Case is created for that Customer - Address, City & Zip should automatically be filled. So that Sales reps don't have to fill those 3 fields again.
Here is my CODE
trigger CasesTrigger on Case (after insert){
    Set<Id> accIds = new Set<Id>();
    List<Case> lstCases = new List<Case>();
    for(Case objCase:trigger.new){
        accIds.add(objCase.AccountId);
        system.debug('ACCOUNTIDS'+accIds);
    }
    Map<ID, Account> MapAccIdtoAccount = new Map<ID, Account>([Select Id, Street__c, City__c, State__c, Zip__c from Account where Id IN:accIds]);
system.debug('ACCOUNTSMAP'+MapAccIdtoAccount);
    for(Case objCase:Trigger.new){
        Case oCase = new Case();
       
    if(MapAccIdtoAccount.containsKey(objCase.AccountId))
{
         oCase.Address_Line1__c = MapAccIdtoAccount.get(oCase.AccountId).Street__c ;
            system.debug('ADDRESS---'+oCase.Address_Line1__c); 
           oCase.City__c = MapAccIdtoAccount.get(oCase.AccountId).City__c ;
            oCase.State__c = MapAccIdtoAccount.get(oCase.AccountId).State__c ;
           oCase.Zip__c = MapAccIdtoAccount.get(oCase.AccountId).Zip__c ;
        lstCases.add(oCase);
         system.debug('oCASE'+oCase); 
            }
            }
    if(lstCases.size()>0){
        update lstCases;
    }
}

Hi,

Could you please help me how to upload excel data in to salesforce, for example if i got data in excel sheet from client i want to upload into salesforce how to achieve this.

Thanks
Mantu

Hi Guys,

1. Until the Spring 15 release, Maps and Sets are Unordered Collections. So the returned order will be random.
2. But beginning from Summer 15 release onwards, Maps and Set order is predictable. The order will be same that what you put from the beginning to end.

Example:
Map<String, String> orderedMap = new Map<String, String>();
orderedMap.put('Good', 'This is so good');
orderedMap.put('Bad', 'This is so bad');
System.debug(orderedMap);

If you run the above code snippet in Developer console you will get the returned order as below,

Until Spring 15 Release:

{Bad=This is so bad, Good=This is so good}

From Summer 15 Release:

{Good=This is so good, Bad=This is so bad}

This changes is not the API level, this is Schema level change. If anyone relying on the Map or Set order in your codes, change it as soon. 

Thanks.