Cache.get(key, type) should also work in case of null value found in cache

Issue: SPR-11567

spring-context/src/test/java/org/springframework/cache/concurrent/ConcurrentCacheTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2013 the original author or authors.
+ * Copyright 2010-2014 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -28,6 +28,7 @@ import static org.junit.Assert.*;
 
 /**
  * @author Costin Leau
+ * @author Juergen Hoeller
  */
 public class ConcurrentCacheTests  {
 
@@ -62,11 +63,20 @@ public class ConcurrentCacheTests  {
 		Object value = "george";
 
 		assertNull(cache.get(key));
+		assertNull(cache.get(key, String.class));
+		assertNull(cache.get(key, Object.class));
+
 		cache.put(key, value);
 		assertEquals(value, cache.get(key).get());
 		assertEquals(value, cache.get(key, String.class));
 		assertEquals(value, cache.get(key, Object.class));
 		assertEquals(value, cache.get(key, null));
+
+		cache.put(key, null);
+		assertNotNull(cache.get(key));
+		assertNull(cache.get(key).get());
+		assertNull(cache.get(key, String.class));
+		assertNull(cache.get(key, Object.class));
 	}
 
 	@Test