diff --git a/core-java-modules/core-java-concurrency-collections-2/src/main/java/com/baeldung/concurrent/lock/SingleLock.java b/core-java-modules/core-java-concurrency-collections-2/src/main/java/com/baeldung/concurrent/lock/SingleLock.java
index 762053c4c9..19b3ba4510 100644
--- a/core-java-modules/core-java-concurrency-collections-2/src/main/java/com/baeldung/concurrent/lock/SingleLock.java
+++ b/core-java-modules/core-java-concurrency-collections-2/src/main/java/com/baeldung/concurrent/lock/SingleLock.java
@@ -16,11 +16,10 @@ public class SingleLock extends ConcurrentAccessExperiment {
         return (()-> {
             try {
                 lock.lock();
-                map.put("key" + key, "value" + key);
+                return map.put("key" + key, "value" + key);
             } finally {
                 lock.unlock();
             }
-            return null;
         });
     }
 
@@ -28,11 +27,10 @@ public class SingleLock extends ConcurrentAccessExperiment {
         return (()-> {
             try {
                 lock.lock();
-                map.get("key" + key);
+                return map.get("key" + key);
             } finally {
                 lock.unlock();
             }
-            return null;
         });
     }
 }
diff --git a/core-java-modules/core-java-concurrency-collections-2/src/main/java/com/baeldung/concurrent/lock/StripedLock.java b/core-java-modules/core-java-concurrency-collections-2/src/main/java/com/baeldung/concurrent/lock/StripedLock.java
index e132cb061d..7adca428ba 100644
--- a/core-java-modules/core-java-concurrency-collections-2/src/main/java/com/baeldung/concurrent/lock/StripedLock.java
+++ b/core-java-modules/core-java-concurrency-collections-2/src/main/java/com/baeldung/concurrent/lock/StripedLock.java
@@ -19,11 +19,10 @@ public class StripedLock extends ConcurrentAccessExperiment {
             Lock lock = stripedLock.get(bucket);
             try {
                 lock.lock();
-                map.put("key" + key, "value" + key);
+                return map.put("key" + key, "value" + key);
             } finally {
                 lock.unlock();
             }
-            return null;
         });
     }
 
@@ -33,11 +32,10 @@ public class StripedLock extends ConcurrentAccessExperiment {
             Lock lock = stripedLock.get(bucket);
             try {
                 lock.lock();
-                map.get("key" + key);
+                return map.get("key" + key);
             } finally {
                 lock.unlock();
             }
-            return null;
         });
     }
 }