FULL PRODUCT VERSION :
  Java 1.8.0_25

ADDITIONAL OS VERSION INFORMATION :
  Windows 8

A DESCRIPTION OF THE PROBLEM :
  If you add a non-comparable object to PriorityQueue it adds the first one, but any other objects throw an exception - but the size increases and a null object is inserted. Which can cause problems if the queue.poll() is called as a NPE occurs.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
  Size is 0
ACTUAL -
  NullPointerException

ERROR MESSAGES/STACK TRACES THAT OCCUR :
  java.lang.NullPointerException
      at java.util.PriorityQueue.siftDownComparable(Unknown Source)
      at java.util.PriorityQueue.siftDown(Unknown Source)
      at java.util.PriorityQueue.poll(Unknown Source)

REPRODUCIBILITY :
  This bug can be reproduced always.

---------- BEGIN SOURCE ----------
    public class NonComparableTest {
        public static void main(String[] args) {
            PriorityQueue<Person> pq = new PriorityQueue<>();
                for (int i=0; i<5; i++) {
                    try {
                        pq.add(new Person());
                    } catch(Exception ignored) { }
                }
                pq.poll();
                System.out.println("The size is " + pq.size());
                for (Iterator<Person> it = pq.iterator(); it.hasNext();) {
                    System.out.println(it.next());
                }
        }
    }

    class Person { }
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
    public boolean offer(E e) {
        if (e == null)
            throw new NullPointerException();
        modCount++;
        int i = size;
        if (i >= queue.length)
            grow(i + 1);
        
        if (i == 0)
            queue[0] = e;
        else
            siftUp(i+1, e);
        size = i + 1; // ONly increase size after adding to queue
        return true;
    }