getting a strange error from intelliJ. Can someone please explain what I've done wrong here? package com.codegym.task.task08.task0819; import java.util.HashSet; import java.util.Iterator; import java.util.Set; /* Set of cats */ public class Solution { public static void main(String[] args) { Set<Cat> cats = createCats(); Set<Cat> copycat = new HashSet<Cat>(cats); Iterator<Cat> it = copycat.iterator(); Cat delete = new Cat(); while (it.hasNext()){ delete = it.next(); cats.remove(delete); break; } printCats(cats); } public static Set<Cat> createCats() { Set<Cat> ccats = new HashSet<Cat>(); Cat james = new Cat(); Cat johnny = new Cat(); Cat boris = new Cat(); ccats.add(james); ccats.add(johnny); ccats.add(boris); return ccats; } public static void printCats(Set<Cat> cats) { for (Cat catlist : cats) { System.out.println(catlist); } } public static class Cat {} }