diff --git a/cas-client-core/src/main/java/org/jasig/cas/client/proxy/ProxyGrantingTicketStorageImpl.java b/cas-client-core/src/main/java/org/jasig/cas/client/proxy/ProxyGrantingTicketStorageImpl.java
index a1d1394..b62592b 100644
--- a/cas-client-core/src/main/java/org/jasig/cas/client/proxy/ProxyGrantingTicketStorageImpl.java
+++ b/cas-client-core/src/main/java/org/jasig/cas/client/proxy/ProxyGrantingTicketStorageImpl.java
@@ -25,6 +25,7 @@ import java.util.concurrent.ConcurrentMap;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.jasig.cas.client.util.CommonUtils;
 
 /**
  * Implementation of {@link ProxyGrantingTicketStorage} that is backed by a
@@ -82,6 +83,10 @@ public final class ProxyGrantingTicketStorageImpl implements ProxyGrantingTicket
      * Its removed after retrieval.
      */
     public String retrieve(final String proxyGrantingTicketIou) {
+        if (CommonUtils.isBlank(proxyGrantingTicketIou)) {
+            return null;
+        }
+
         final ProxyGrantingTicketHolder holder = this.cache.get(proxyGrantingTicketIou);
 
         if (holder == null) {
diff --git a/cas-client-core/src/test/java/org/jasig/cas/client/proxy/ProxyGrantingTicketStorageImplTest.java b/cas-client-core/src/test/java/org/jasig/cas/client/proxy/ProxyGrantingTicketStorageImplTest.java
index 21b31d5..746ada9 100644
--- a/cas-client-core/src/test/java/org/jasig/cas/client/proxy/ProxyGrantingTicketStorageImplTest.java
+++ b/cas-client-core/src/test/java/org/jasig/cas/client/proxy/ProxyGrantingTicketStorageImplTest.java
@@ -20,25 +20,37 @@
 package org.jasig.cas.client.proxy;
 
 import junit.framework.TestCase;
+import org.junit.Assert;
+import org.junit.Test;
 
 /**
  * Unit test for {@link ProxyGrantingTicketStorageImpl}
  * 
  * @author Brad Cupit (brad [at] lsu {dot} edu)
  */
-public class ProxyGrantingTicketStorageImplTest extends TestCase {
-    public void testCleanUp() throws Exception {
+public class ProxyGrantingTicketStorageImplTest {
+
+    private static final int TIME_OUT = 250;
+
+    private ProxyGrantingTicketStorage storage = new ProxyGrantingTicketStorageImpl(TIME_OUT);
+
+    @Test
+    public void cleanUp() throws Exception {
         String proxyGrantingTicketIou = "proxyGrantingTicketIou";
         
         int timeout = 250;
-        ProxyGrantingTicketStorageImpl storage = new ProxyGrantingTicketStorageImpl(timeout);
-        storage.save(proxyGrantingTicketIou, "proxyGrantingTicket");
+        this.storage.save(proxyGrantingTicketIou, "proxyGrantingTicket");
         
         // sleep long enough for the ticket to timeout
         Thread.sleep(timeout * 2);
         
-        storage.cleanUp();
+        this.storage.cleanUp();
         
-        assertNull(storage.retrieve(proxyGrantingTicketIou));
+        Assert.assertNull(this.storage.retrieve(proxyGrantingTicketIou));
+    }
+
+    @Test
+    public void nullPGTIOU() {
+        Assert.assertNull(this.storage.retrieve(null));
     }
 }