Merge branch 'hotfix/4199' into develop

Forward port zendframework/zendframework#4199

src/PriorityQueue.php

@@ -98,9 +98,12 @@ public function remove($datum)
         if ($found) {
             unset($this->items[$key]);
             $this->queue = null;
-            $queue = $this->getQueue();
-            foreach ($this->items as $item) {
-                $queue->insert($item['data'], $item['priority']);
+
+            if (!$this->isEmpty()) {
+                $queue = $this->getQueue();
+                foreach ($this->items as $item) {
+                    $queue->insert($item['data'], $item['priority']);
+                }
             }
             return true;
         }

test/PriorityQueueTest.php

@@ -151,4 +151,18 @@ public function testCloningAlsoClonesQueue()
 
         $this->assertTrue($queueClone->isEmpty());
     }
+
+    public function testQueueRevertsToInitialStateWhenEmpty()
+    {
+        $queue = new PriorityQueue();
+        $testQueue = clone $queue; // store the default state
+
+        $testQueue->insert('foo', 1);
+        $testQueue->insert('bar', 2);
+
+        $testQueue->remove('foo');
+        $testQueue->remove('bar');
+
+        $this->assertEquals($queue, $testQueue);
+    }
 }