Trigger Update causes System.null pointer Exception

Question

Trigger on document Object. Whenever I update document its populating corresponding platform name on document level.

 trigger s360_DocumentSOSLTrigger on Document__c (before insert,before update) {
if((trigger.isInsert || trigger.isUpdate) && trigger.isBefore){
    S360_DocumentDetails.documentupdate(trigger.new);
}}

---

  public class S360_DocumentDetails {
public static void documentupdate(List<Document__c> docList){
     set<id> Platformset=new set<id>();
    for(Document__c doc:docList){
        if(doc.Platform__c!=null){
             Platformset.add(doc.Platform__c);
        }

    }
    map<id,Platform__c> paltformmap=new map<id,Platform__c>();
    for(Platform__c plat:[select id,Aircraft_Manufacturer__c,name from Platform__c where Id in:Platformset]){
        paltformmap.put(plat.id,plat);
    }

    for(Document__c D2:docList){
     if(paltformmap.get(D2.Platform__c).name!=null && 
      plaformmap.containskey(D2.Platform__c)){
           D2.PlatformSOSL__c=paltformmap.get(D2.Platform__c).name;
        }else
        {  
            D2.PlatformSOSL__c='';
        }

    }
    }}

Issue facing:

I have executed following code in Anonymous window. before that what I did I just updated "platform" in document level. For perticular that platform I got the error:

Script I have executed in Anonymous window:

  List<Document__c> docList=[select 
 Id,Platform__c,Platform__r.name,Revision__c,Send_Revision_Email__c from 
     Document__c];
  List<Document__c> doclist1=new List<Document__c>();
 for(Document__c doc:docList){
  doc.Send_Revision_Email__c=true;
  doclist1.add(doc);
}
update doclist1;

Error Image:

Answer 1

In your second for loop add check of add check ofD2.Platform__c != null as you are checking null for this in first for loop so chances are it is coming null and you are getting this exception.

Answer 2

You need to check if the map contains the key before accessing its data. Use the below code.

public class S360_DocumentDetails {
public static void documentupdate(List<Document__c> docList){
     set<id> Platformset=new set<id>();
    for(Document__c doc:docList){
        if(doc.Platform__c!=null){
             Platformset.add(doc.Platform__c);
        }

    }
    map<id,Platform__c> paltformmap=new map<id,Platform__c>();
    for(Platform__c plat:[select id,Aircraft_Manufacturer__c,name from Platform__c where Id in:Platformset]){
        paltformmap.put(plat.id,plat);
    }

    for(Document__c D2:docList){
        if (paltformmap.containsKey(D2.Platform__c)) {
            D2.PlatformSOSL__c=paltformmap.get(D2.Platform__c).name;
            D2.AircraftManufacturerSOSL__c=paltformmap.get(D2.Platform__c).Aircraft_Manufacturer__c;
        }
    }
}

Here you can see I have used the Map.containsKey(Id) to check if the map contains this key or not. By doing this we won't face null exception.