push(key);
}
return this;
}
public Object peek() {
<BUG>return history.isEmpty() ? null : history.get(history.size() - 1).getKey();
}</BUG>
public boolean isEmpty() {
return history.isEmpty();
}

push(key);
}
return this;
}
public Object peek() {
return history.isEmpty() ? null : history.get(history.size() - 1);
}
public boolean isEmpty() {
return history.isEmpty();
}
