My requirement was Latest opportunity name should be displayed in account object custom field.

Getting null pointer exception when I delete the opportunity for the Account. How do we handle this error.

Class :

public class OppAccUpdate
{
  
  public void oppupdate(List<opportunity> oplist)
  {
      
    set<id> accid = new set<id>();
    
   // List<Account> acctoUpdate= new List<Account>();
   
   Map<id,Account> mapaccounts = new Map<id,Account>();
    
    for(opportunity opp:oplist)
    {
       accid.add(opp.Accountid);
    }
    List<Account> acc =[select id, oppname__c,(select id, name from opportunities order by createddate) from Account where id in:accid];
    system.debug('****Thesize of account***'+acc.size());
    system.debug('****The oppname***'+acc[0].oppname__c);
    system.debug('****The opportunity***'+acc[0].opportunities);
    for(Account a:acc)
    {
       for(opportunity o:a.Opportunities)
       {
          if(a.oppname__c==null || (a.oppname__c!=o.Name))
          {
          system.debug('***inside for loop***'+ a.oppname__c);
          system.debug('***inside for loop111***'+ o.name);
          a.oppname__c = o.Name;
          mapaccounts.put(a.id,a);
         // acctoUpdate.add(a);
          }
       }
    }
    if(!mapaccounts.isEmpty())
    update  mapaccounts.values();

      
  }
}

Trigger:

trigger oppaccupdate on Opportunity (after insert, After update, After delete) 
{
     Opportunity[] opp = trigger.new;
     
     if(trigger.isInsert || trigger.isAfter)
     {
       OppAccUpdate ou = new OppAccUpdate();
       ou.oppupdate(opp);
     }
     
      if(trigger.isUpdate || trigger.isAfter)
     {
       OppAccUpdate ou = new OppAccUpdate();
       ou.oppupdate(opp);
     }
     
      if(trigger.isDelete || trigger.isAfter)
     {
       Opportunity[] opp1 = trigger.old;
       OppAccUpdate ou = new OppAccUpdate();
       ou.oppupdate(opp1);
     }
}