I'm receiving an error when attempting to run my test class. jstcl__Placement__c is a lookup who's parent is ts2__Placement__c which is why I construct it initially.

Error:
System.DmlException: Insert failed. First exception on row 0; first error: CANNOT_INSERT_UPDATE_ACTIVATE_ENTITY, ts2.Placement: execution of BeforeInsert caused by: System.NullPointerException: Attempt to de-reference a null object Trigger.ts2.Placement: line 14, column 1: []
 

@istest
public class placementTimecardAuditFlagTest{
    
     static testMethod void myTest() {
         
		Contact a= new Contact(Lastname = 'Test');
		insert a;
        
        ts2__Placement__c b= new ts2__Placement__c();
        insert b;
 
// Create common test timesheets
        List<jstcl__TG_Timesheet__c> testTimesheets = new List<jstcl__TG_Timesheet__c>();
        for(Integer i=0 ;i <200;i++) { 			
            testTimesheets.add(new jstcl__TG_Timesheet__c(jstcl__Week_Ending__c = Date.today()-15, jstcl__Consultant__c = a.Id,jstcl__Placement__c=b.Name));
        }
        insert testTimesheets;       

         
// Create common test placements
        List<ts2__Placement__c> testPlacements = new List<ts2__Placement__c>();
        for(Integer i=0 ;i <200;i++) {
            testPlacements.add(new ts2__Placement__c(ts2__Status__c = 'Active'));

        }
        insert testPlacements;        
//Testing
    Test.startTest();  
        
      placementTimecardAuditFlag obj = new placementTimecardAuditFlag();
        DataBase.executeBatch(obj); 
        
        Test.stopTest();
        System.AssertEquals(database.countquery('SELECT TCEDaudit__c FROM ts2__Placement__c'),1);
    }}