I have a apex extension class that is supposed to save data from a visualforce page into several different objects.  The main object is contract, but the class should also update the account, opportunity, and a custom object called NSA_Agencies__c.  The NSA_Agencies__c field is not a required lookup field, so when I try to save a contract that has no agency, I get an exception - Attempt to de-reference a null object

How do I code my controller extension to only save if that lookup field is populated?  If not populated, the code should ignore that part of the save function.

Here is my extension:

public

withsharingclassRPM_Credit {

ApexPages.StandardController controller;

publicContract contract {get; set;}

publicOpportunity opportunity {get; set;}

publicAccount account {get; set;}

publicNSA_Agencies__c agency {get; set;}

public

RPM_Credit(ApexPages.StandardController con){

controller = con;

contract = (

Contract) controller.getRecord();

opportunity = contract.Opportunity__r;

account = contract.account;

agency = contract.account.RPM_NSA_Agency__r;

}

publicPageReference saveall() {

updateopportunity;

updateaccount;

updateagency;

controller.save();

PageReference pageRef =

new PageReference('https://na5.salesforce.com/00O70000003JDRo');

returnnull;

}

}

Thank you!!