Help with using iterator remove on double linked list

I am trying to remove data from a double linked list using the remove method using a iterator and I keep getting a null pointer exception.

This is what I have

System.out.print("Enter student ID: ");
String studentID2 = in.next();
Iterator<Student> iter = students.iterator();
while (iter.hasNext()) {
Student stu = (Student) iter.next();
if(stu.getStudentID().equals(studentID2)){
iter.remove();
}
}

Says the error is in my remove method

public void remove() {
lastItemRet = lastItemRet.prev;
lastItemRet.next = nextItem; The error is on this line.
nextItem.prev = lastItemRet;
}

Post an SSCCE and the full error code, or else you get guesses. My guess, nextItem is not defined anywhere or is out of scope of the location you are trying to access it.

The full error I get isThe full error I get is


Exception in thread "main" java.lang.NullPointerException
at DLList$Node.access$3(DLList.java:105)
at DLList$ListIter.remove(DLList.java:182)
at Menu.display(Menu.java:46)
at Prog3.main(Prog3.java:17)

What could be null on that line? Could lastItemRet be null? Add some println's in there to try and debug, or use a debugger to step through the code and see what is null. Without an SSCCE it is hard to comment on a fix.