Allow caching null objects.

src/main/java/org/springframework/data/couchbase/cache/CouchbaseCache.java

@@ -106,7 +106,7 @@ public void put(final Object key, final Object value) {
 					name));
 		}
 
-		cacheWriter.put(cacheConfig.getCollectionName(), createCacheKey(key), value, cacheConfig.getExpiry(),
+		cacheWriter.put(cacheConfig.getCollectionName(), createCacheKey(key), toStoreValue(value), cacheConfig.getExpiry(),
 				cacheConfig.getValueTranscoder());
 	}
 
@@ -116,7 +116,7 @@ public ValueWrapper putIfAbsent(final Object key, final Object value) {
 			return get(key);
 		}
 
-		Object result = cacheWriter.putIfAbsent(cacheConfig.getCollectionName(), createCacheKey(key), value,
+		Object result = cacheWriter.putIfAbsent(cacheConfig.getCollectionName(), createCacheKey(key), toStoreValue(value),
 				cacheConfig.getExpiry(), cacheConfig.getValueTranscoder());
 
 		if (result == null) {

src/test/java/org/springframework/data/couchbase/cache/CacheUser.java

@@ -0,0 +1,71 @@
+/*
+ * Copyright 2022 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.
+ * You may obtain a copy of the License at
+ *
+ *        https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.couchbase.cache;
+
+import java.io.Serializable;
+
+/**
+ * This is a standalone class (vs. inner) to allow Serialization of all fields to work.
+ * If it was an inner class of CouchbaseCacheIntegrationTests, then it would have a
+ * this$0 field = CouchbaseCacheIntegrationTests and would not serialize.
+ *
+ * @author Michael Reiche
+ */
+class CacheUser implements Serializable {
+	// private static final long serialVersionUID = 8817717605659870262L;
+	String firstname;
+	String lastname;
+	String id;
+
+	public CacheUser(String id, String firstname, String lastname) {
+		this.id = id;
+		this.firstname = firstname;
+		this.lastname = lastname;
+	}
+
+	public String getId() {
+		return id;
+	}
+
+	// define equals for assertEquals()
+	public boolean equals(Object o) {
+		if (o == null) {
+			return false;
+		}
+		if (!(o instanceof CacheUser)) {
+			return false;
+		}
+
+		CacheUser other = (CacheUser) o;
+		if (id == null && other.id != null) {
+			return false;
+		}
+		if (firstname == null && other.firstname != null) {
+			return false;
+		}
+		if (lastname == null && other.lastname != null) {
+			return false;
+		}
+		return id.equals(other.id) && firstname.equals(other.firstname) && lastname.equals(other.lastname);
+	}
+
+	public String toString() {
+		StringBuffer sb = new StringBuffer();
+		sb.append("CacheUser: { id=" + id + ", firstname=" + firstname + ", lastname=" + lastname + "}");
+		return sb.toString();
+	}
+
+}

src/test/java/org/springframework/data/couchbase/cache/CouchbaseCacheIntegrationTests.java

@@ -0,0 +1,101 @@
+/*
+ * Copyright 2022 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.
+ * You may obtain a copy of the License at
+ *
+ *        https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.data.couchbase.cache;
+
+import static com.couchbase.client.java.query.QueryScanConsistency.REQUEST_PLUS;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+import java.util.UUID;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.springframework.data.couchbase.util.ClusterType;
+import org.springframework.data.couchbase.util.IgnoreWhen;
+import org.springframework.data.couchbase.util.JavaIntegrationTests;
+
+import com.couchbase.client.java.query.QueryOptions;
+
+/**
+ * CouchbaseCache tests Theses tests rely on a cb server running.
+ *
+ * @author Michael Reiche
+ */
+@IgnoreWhen(clusterTypes = ClusterType.MOCKED)
+class CouchbaseCacheIntegrationTests extends JavaIntegrationTests {
+
+	volatile CouchbaseCache cache;
+
+	@BeforeEach
+	@Override
+	public void beforeEach() {
+		super.beforeEach();
+		cache = CouchbaseCacheManager.create(couchbaseTemplate.getCouchbaseClientFactory()).createCouchbaseCache("myCache",
+				CouchbaseCacheConfiguration.defaultCacheConfig());
+		clear(cache);
+	}
+
+	private void clear(CouchbaseCache c) {
+		couchbaseTemplate.getCouchbaseClientFactory().getCluster().query("SELECT count(*) from `" + bucketName() + "`",
+				QueryOptions.queryOptions().scanConsistency(REQUEST_PLUS));
+		c.clear();
+		couchbaseTemplate.getCouchbaseClientFactory().getCluster().query("SELECT count(*) from `" + bucketName() + "`",
+				QueryOptions.queryOptions().scanConsistency(REQUEST_PLUS));
+	}
+
+	@Test
+	void cachePutGet() {
+		CacheUser user1 = new CacheUser(UUID.randomUUID().toString(), "first1", "last1");
+		CacheUser user2 = new CacheUser(UUID.randomUUID().toString(), "first2", "last2");
+		assertNull(cache.get(user1.getId())); // was not put -> cacheMiss
+		cache.put(user1.getId(), user1); // put user1
+		cache.put(user2.getId(), user2); // put user2
+		assertEquals(user1, cache.get(user1.getId()).get()); // get user1
+		assertEquals(user2, cache.get(user2.getId()).get()); // get user2
+	}
+
+	@Test
+	void cacheEvict() {
+		CacheUser user1 = new CacheUser(UUID.randomUUID().toString(), "first1", "last1");
+		CacheUser user2 = new CacheUser(UUID.randomUUID().toString(), "first2", "last2");
+		cache.put(user1.getId(), user1); // put user1
+		cache.put(user2.getId(), user2); // put user2
+		cache.evict(user1.getId()); // evict user1
+		assertEquals(user2, cache.get(user2.getId()).get()); // get user2 -> present
+	}
+
+	@Test
+	void cacheHitMiss() {
+		CacheUser user1 = new CacheUser(UUID.randomUUID().toString(), "first1", "last1");
+		CacheUser user2 = new CacheUser(UUID.randomUUID().toString(), "first2", "last2");
+		assertNull(cache.get(user2.getId())); // get user2 -> cacheMiss
+		cache.put(user1.getId(), null); // cache a null
+		assertNotNull(cache.get(user1.getId())); // cacheHit null
+		assertNull(cache.get(user1.getId()).get()); // fetch cached null
+	}
+
+	@Test
+	void cachePutIfAbsent() {
+		CacheUser user1 = new CacheUser(UUID.randomUUID().toString(), "first1", "last1");
+		CacheUser user2 = new CacheUser(UUID.randomUUID().toString(), "first2", "last2");
+		assertNull(cache.putIfAbsent(user1.getId(), user1)); // should put user1, return null
+		assertEquals(user1, cache.putIfAbsent(user1.getId(), user2).get()); // should not put user2, should return user1
+		assertEquals(user1, cache.get(user1.getId()).get()); // user1.getId() is still user1
+	}
+
+}