diff --git a/bundles/org.openhab.core.thing/src/main/java/org/openhab/core/thing/util/ThingHandlerHelper.java b/bundles/org.openhab.core.thing/src/main/java/org/openhab/core/thing/util/ThingHandlerHelper.java
index 9233a4294..86c438fd5 100644
--- a/bundles/org.openhab.core.thing/src/main/java/org/openhab/core/thing/util/ThingHandlerHelper.java
+++ b/bundles/org.openhab.core.thing/src/main/java/org/openhab/core/thing/util/ThingHandlerHelper.java
@@ -12,6 +12,7 @@
  */
 package org.openhab.core.thing.util;
 
+import org.eclipse.jdt.annotation.NonNullByDefault;
 import org.openhab.core.thing.Thing;
 import org.openhab.core.thing.ThingStatus;
 import org.openhab.core.thing.binding.ThingHandler;
@@ -22,6 +23,7 @@ import org.openhab.core.thing.binding.ThingHandler;
  * @author Markus Rathgeb - Initial contribution
  * @author Simon Kaufmann - added UNKNOWN
  */
+@NonNullByDefault
 public class ThingHandlerHelper {
 
     private ThingHandlerHelper() {
diff --git a/itests/org.openhab.core.thing.tests/src/main/java/org/openhab/core/thing/internal/ChannelLinkNotifierOSGiTest.java b/itests/org.openhab.core.thing.tests/src/main/java/org/openhab/core/thing/internal/ChannelLinkNotifierOSGiTest.java
index a222fccd8..22b7edd5b 100644
--- a/itests/org.openhab.core.thing.tests/src/main/java/org/openhab/core/thing/internal/ChannelLinkNotifierOSGiTest.java
+++ b/itests/org.openhab.core.thing.tests/src/main/java/org/openhab/core/thing/internal/ChannelLinkNotifierOSGiTest.java
@@ -18,7 +18,6 @@ import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.when;
 import static org.mockito.MockitoAnnotations.openMocks;
-import static org.openhab.core.thing.util.ThingHandlerHelper.isHandlerInitialized;
 
 import java.util.ArrayList;
 import java.util.HashMap;
@@ -58,6 +57,7 @@ import org.openhab.core.thing.link.ItemChannelLinkRegistry;
 import org.openhab.core.thing.link.ManagedItemChannelLinkProvider;
 import org.openhab.core.thing.type.ChannelKind;
 import org.openhab.core.thing.type.ChannelTypeUID;
+import org.openhab.core.thing.util.ThingHandlerHelper;
 import org.openhab.core.types.Command;
 import org.openhab.core.util.BundleResolver;
 import org.osgi.framework.Bundle;
@@ -96,7 +96,7 @@ public class ChannelLinkNotifierOSGiTest extends JavaOSGiTest {
 
         private final @Nullable ThingStatus thingStatus;
 
-        private Map<ChannelUID, List<Boolean>> channelLinkEvents = new HashMap<>();
+        private final Map<ChannelUID, List<Boolean>> channelLinkEvents = new HashMap<>();
 
         public TestHandler(Thing thing, @Nullable ThingStatus thingStatus) {
             super(thing);
@@ -118,12 +118,12 @@ public class ChannelLinkNotifierOSGiTest extends JavaOSGiTest {
 
         @Override
         public void channelLinked(ChannelUID channelUID) {
-            channelLinkEvents.get(channelUID).add(Boolean.TRUE);
+            channelLinkEvents.getOrDefault(channelUID, List.of()).add(Boolean.TRUE);
         }
 
         @Override
         public void channelUnlinked(ChannelUID channelUID) {
-            channelLinkEvents.get(channelUID).add(Boolean.FALSE);
+            channelLinkEvents.getOrDefault(channelUID, List.of()).add(Boolean.FALSE);
         }
 
         public List<Boolean> getChannelLinkEvents(ChannelUID channelUID) {
@@ -208,13 +208,13 @@ public class ChannelLinkNotifierOSGiTest extends JavaOSGiTest {
 
     private Thing addInitializedThing() {
         Thing thing = addThing(ThingStatus.ONLINE);
-        assertThat(isHandlerInitialized(thing.getHandler()), is(true));
+        assertThat(ThingHandlerHelper.isHandlerInitialized(getHandler(thing)), is(true));
         return thing;
     }
 
     private Thing addUninitializedThing() {
         Thing thing = addThing(null);
-        assertThat(isHandlerInitialized(thing.getHandler()), is(false));
+        assertThat(ThingHandlerHelper.isHandlerInitialized(getHandler(thing)), is(false));
         return thing;
     }