spliterator iterator methods added to students and instructors

demo/src/main/java/com/example/demo/Instructors.java

@@ -17,7 +17,7 @@ public class Instructors extends People<Instructor> {
 
     @Override
     public Iterator iterator() {
-        return null;
+        return this.personList.iterator();
     }
 
     @Override
@@ -27,6 +27,6 @@ public class Instructors extends People<Instructor> {
 
     @Override
     public Spliterator spliterator() {
-        return null;
+        return this.personList.spliterator();
     }
 }