Inline VF Page is returning Attempt to De-Reference Null Object Error

Question

I'm experimenting with the code below from another post on stackexchange:

All I'm trying to do is display a VF box in Opportunities to instruct Users on what to do at each stage. It uses a custom object, controller and a VF page. The custom object holds 2 fields, one for the stage and another for the instructions. I have made a few changes, but nothing major. For some reason, when I test the VF page I get the following error:

Content cannot be displayed: Attempt to de-reference a null object

I have created new records in the custom object that match the stage names in the opportunity object.

Can anyone help?

Controller Code:

public class OppInstructionsController {

    public Opportunity opp                                              {get;set;}
    public list<Opportunity_Helper__c> myRules                          {get;set;}
    public map<string,string> stage2Instructions                        {get;set;}
    public string StageInstructions                                     {get;set;}      

    public OppInstructionsController(ApexPages.StandardController controller){
        this.opp= (Opportunity)controller.getRecord();
        myRules = [Select Id, StageName__c, Instructions__c From Opportunity_Helper__c]; 
        for(Opportunity_Helper__c rule : myRules){
            stage2Instructions.put(rule.StageName__c, rule.Instructions__c);
        }

        StageInstructions = stage2Instructions.get(this.opp.StageName);                 
    }       
}

VF Page:

<apex:page StandardController="Opportunity" extensions="OppInstructionsController">
<apex:outputText value="{!StageInstructions}"/>
</apex:page>

Answer 1

You have not initialized the Map stage2Instructions. You will not be able to add values to to it unless you initialize it and also before accessing a value from the map it is always essential to check if the key is present in the map. You can change your constructor code something like this:

//initialize your map
stage2Instructions = new Map<String, String>();
for(Opportunity_Helper__c rule : myRules){
    stage2Instructions.put(rule.StageName__c, rule.Instructions__c);
}
//check if the key exists
if(stage2Instructions.containsKey(this.opp.StageName)){
    StageInstructions = stage2Instructions.get(this.opp.StageName);
}else {
    StageInstructions = 'setSomeDefaultValue';
}

But in your case you can change your code to execute something like this, which also does pretty much what you're doing without having to use maps.

try{
    stageInstructions = [Select Id, StageName__c, Instructions__c From Opportunity_Helper__c Where StageName__c=:opp.stageName LIMIT 1].Instructions__c;
}
//in case the SOQl has no records returned it throws an exception. 
catch(exception e) {

    stageInstructions = 'setSomeDefaultValue';
}

Answer 2

Try doing this- Your query might not returning any result OR Map is empty

Your Code line :

StageInstructions = stage2Instructions.get(this.opp.StageName);

Replace with following Code Snippet :

 if(stage2Instructions.size()>0){
       System.Debug('-----My Map is not Empty ---');
        StageInstructions = stage2Instructions.get(this.opp.StageName); 
    }