employee==>API:  junebatch2021__Employee__c

employee payment==>API: junebatch2021__EMP_PAYMENT__c

Both in Lookup r/s where employee is parent.

Now,
employee payment there is a amount field soas many time i enter amount corresponding to there employee it will rollup and Relect
the SUM IN 

Total field :API==>junebatch2021__Total__c
WHICH IS CURRENCY FIELD ON PARENT OBJECT WITH DEFAULT VALUE 0.


I AM POSTING ERROR AND BELOW THAT MY HANDLER AND TRIGGER,,,
IF ANY ONE CAN GIVE SOME VALUABLE FEEDBACK ,,THAT WOULD BE VERY HELPFULL.

Error: Invalid Data. 
Review all error messages below to correct your data.
Apex trigger junebatch2021.deleteAction caused an unexpected exception, contact your administrator: junebatch2021.deleteAction: execution of BeforeInsert caused by: System.NullPointerException: Attempt to de-reference a null object: Class.junebatch2021.deleteAction.del: line 3, column 1





Handler:

public class EmpLaymentHelper {
    public static void beforeInsert(List<junebatch2021__EMP_PAYMENT__c> payments){
        for(junebatch2021__EMP_PAYMENT__c p:payments){
            if(p.junebatch2021__Employee__c==null){
                p.junebatch2021__Employee__c.addError('SELECT THE EMPLOYEE');
            }
        }
    }
    public static void afterInsert(List<junebatch2021__EMP_PAYMENT__c> payments){
        Map<Id,List<junebatch2021__EMP_PAYMENT__c>> payMap=new Map<Id,List<junebatch2021__EMP_PAYMENT__c>>();
        try{
        for(junebatch2021__EMP_PAYMENT__c p:payments){
            ID empId=p.junebatch2021__Employee__c;
           Boolean flag=payMap.containsKey(empId);
           List<junebatch2021__EMP_PAYMENT__c> payList=new List<junebatch2021__EMP_PAYMENT__c>();
            
            if(flag==True){
              payList=payMap.get(empId);
              payList.add(p);
              payMap.put(empId,payList);  
            }else{
                payList.add(p);
              payMap.put(empId,payList);   
            }
        }
        
        //LOGIC OF SUM IN CHILD
        
       Map<Id,Decimal> empMap=new Map<Id,Decimal>();
        for(Id key:payMap.keySet()){
            List<junebatch2021__EMP_PAYMENT__c> pays=payMap.get(key);
            Decimal sum=0;
            for(junebatch2021__EMP_PAYMENT__c pa:pays){
                sum=sum+pa.junebatch2021__EMP_AMOUNT__c;
            }
            empMap.put(key,sum);
        }
//NOW REFLECT THAT UPDATE IN PARENT
        
List<junebatch2021__Employee__c> employees=[Select id,junebatch2021__Total__c from junebatch2021__Employee__c where id in:empMap.keySet()];        
        for(junebatch2021__Employee__c e:employees){
          e.junebatch2021__Total__c=e.junebatch2021__Total__c+empMap.get(e.Id);  
        }       
update employees;
    } 
         catch(Exception e){
        e.getMessage();
    }
}
    
   
}



Trigger:

trigger EmpLaymentHelper on junebatch2021__EMP_PAYMENT__c (before insert,after insert,after update,after delete) {
    if(Trigger.isBefore && Trigger.isInsert){
        EmpLaymentHelper.beforeInsert(Trigger.new);
    }
    else{
        if(Trigger.isAfter && Trigger.isInsert){
            EmpLaymentHelper.afterInsert(Trigger.new);
        }
    }
}