Hi All ,

I am getting the following error while deploying a trigger
System.DmlException: Insert failed. First exception on row 0; first error: CANNOT_INSERT_UPDATE_ACTIVATE_ENTITY, ActivityTrigger: execution of AfterInsert caused by: System.NullPointerException: Attempt to de-reference a null object Class.ActivityTriggerHandler.getContactIds: line 17, column 1 Class.ActivityTriggerHandler.updateCallCount: line 7, column 1 Trigger.ActivityTrigger: line 3, column 1: []
Stack Trace: Class.TestUpdateAccountEngScore.myUnitTest: line 61, column 1

This my trigger handler -

public class ActivityTriggerHandler {
    private final String SUB_CATEGORY_CALL = 'Call';
    private final String SUB_CATEGORY_UPDATE = 'Update';
    private final String CONTACT_API = 'Contact';
    
    public void updateCallCount(List<Task> taskList) {
        Set<Id> contactIdSet = getContactIds(taskList);
        List<Contact> contactList = [SELECT Call_Count__c FROM Contact WHERE Id IN :contactIdSet];
        updateContacts(contactList);
    }
    
    private Set<Id> getContactIds(List<Task> taskList) {
        Set<Id> contactIdSet = new Set<Id>();
        for(Task t : taskList) {
            if(t.Sub_Category__c == SUB_CATEGORY_CALL | t.Sub_Category__c == SUB_CATEGORY_UPDATE) {
                Id whoId = t.WhoId;
                if(whoId.getSObjectType().getDescribe().getName() == CONTACT_API)
                    contactIdSet.add(whoId);
            }
        }
        return contactIdSet;
    }
    
    private void updateContacts(List<Contact> contactList) {
        for(Contact con : contactList) {
            if(con.Call_Count__c == NULL || con.Call_Count__c == 0)
                con.Call_Count__c = 1;
            else if(con.Call_Count__c >= 1)
                con.Call_Count__c = con.Call_Count__c + 1;
        }
        update contactList;
    }
}

and this is my trigger

trigger ActivityTrigger on Task (after insert, after update) {
    ActivityTriggerHandler handler = new ActivityTriggerHandler();
    handler.updateCallCount(Trigger.New);
}

Please help me resolve this.