title: PassiveExpiringMap not expiring objects
body: <p>I was expecting org.apache.commons.collections4.map.PassiveExpiringMap to work out of the box. Unfortunately it doesn't work for me in the most obvious use case of expiring objects on time. The code below creates an expiration policy of 5 seconds. The test waits for 10 seconds which is a time by which all map object should be expired and removed. But they're not.</p>
  <pre><code>import org.apache.commons.collections4.map.PassiveExpiringMap;
  import org.junit.Assert;
  import org.junit.Test;
  
  import java.util.HashMap;
  import java.util.Map;
  import java.util.concurrent.TimeUnit;
      
  public class PassiveExpiringMapTest {
      @Test
      public void givenDataMap_whenWrappingMapWithPassiveExpiringMap_thenObjectsAreRemovedWhenExpired() {
          
          final Map&lt;String, Integer&gt; m = new HashMap&lt;&gt;();
          m.put(&quot;one&quot;, Integer.valueOf(1));
          m.put(&quot;two&quot;, Integer.valueOf(2));
          m.put(&quot;three&quot;, Integer.valueOf(3));
  
          PassiveExpiringMap.ConstantTimeToLiveExpirationPolicy&lt;String, Integer&gt;
              expirationPolicy = new PassiveExpiringMap.ConstantTimeToLiveExpirationPolicy&lt;&gt;(
              5, TimeUnit.SECONDS);
  
          PassiveExpiringMap&lt;String, Integer&gt; expiringMap = new PassiveExpiringMap&lt;&gt;(expirationPolicy, m);
  
          int initialCapacity = expiringMap.size();
          System.out.println(&quot;initialCapacity = &quot; + initialCapacity);
          Assert.assertEquals(3, initialCapacity);
  
          System.out.println(&quot;Sleeping...&quot;);
          try { Thread.sleep(10000L); } catch (InterruptedException e) { }
  
          int updatedCapacity = expiringMap.size();
          System.out.println(&quot;updatedCapacity = &quot; + updatedCapacity);
          Integer one = expiringMap.get(&quot;one&quot;);
          Assert.assertNull(one);
          Assert.assertEquals(0, updatedCapacity);
      }
  }
  </code></pre>
  <p>The test fails with the following output:</p>
  <pre><code>initialCapacity = 3
  Sleeping...
  updatedCapacity = 3
  
  java.lang.AssertionError: expected null, but was:&lt;1&gt;
  
      at org.junit.Assert.fail(Assert.java:88)
      at org.junit.Assert.failNotNull(Assert.java:755)
      at org.junit.Assert.assertNull(Assert.java:737)
      at org.junit.Assert.assertNull(Assert.java:747)
  </code></pre>
  <p>Any idea what I am missing?</p>