Updating the Custom Object - Attempt to de-reference a null object

Question

I got stuck and now sure what I'm doing wrong here:

here is my trigger:

trigger EmployeeTrigger on Employee__c (after insert, before update) 
{
    EmployeeController mr = new EmployeeController();
    mr.EmployeeController(Trigger.new);
}

Apex class:

List<Employee__c> Employees = new List<Employee__c>();
List<Employee__c> empList = [SELECT Id, Name, Employee_Name__c
                                     FROM Employee__c 
                                     WHERE Employee_Id__c = 123456 ];

for(Employee__c pm : empList)
{
   pm.Current_City__c = 'timbaktu';
   Employees.Add(pm);
}
update Employees;

Review all error messages below to correct your data. Apex trigger EmployeeTrigger caused an unexpected exception, contact your administrator: EmployeeTrigger: execution of BeforeUpdate caused by: System.NullPointerException: Attempt to de-reference a null object: Class.EmployeeController.EmployeeController: line 147, column 1

Answer 1

If line 147 has pm.Current_City__c = 'timbaktu';, then you probably have this issue because the field Current_City__c was not included in the query.