diff --git a/bundles/org.openhab.automation.jsscripting/src/main/java/org/openhab/automation/jsscripting/internal/GraalJSScriptEngineFactory.java b/bundles/org.openhab.automation.jsscripting/src/main/java/org/openhab/automation/jsscripting/internal/GraalJSScriptEngineFactory.java
index 16d0625f09323..1bdd8a23779ad 100644
--- a/bundles/org.openhab.automation.jsscripting/src/main/java/org/openhab/automation/jsscripting/internal/GraalJSScriptEngineFactory.java
+++ b/bundles/org.openhab.automation.jsscripting/src/main/java/org/openhab/automation/jsscripting/internal/GraalJSScriptEngineFactory.java
@@ -17,6 +17,7 @@
 
 import javax.script.ScriptEngine;
 
+import org.eclipse.jdt.annotation.NonNullByDefault;
 import org.eclipse.jdt.annotation.Nullable;
 import org.openhab.automation.jsscripting.internal.fs.watch.JSDependencyTracker;
 import org.openhab.core.automation.module.script.ScriptDependencyTracker;
@@ -37,6 +38,7 @@
 @Component(service = ScriptEngineFactory.class, configurationPid = "org.openhab.jsscripting", property = Constants.SERVICE_PID
         + "=org.openhab.jsscripting")
 @ConfigurableService(category = "automation", label = "JS Scripting", description_uri = "automation:jsscripting")
+@NonNullByDefault
 public final class GraalJSScriptEngineFactory implements ScriptEngineFactory {
     private static final String CFG_INJECTION_ENABLED = "injectionEnabled";
     private static final String INJECTION_CODE = "Object.assign(this, require('openhab'));";
@@ -80,7 +82,7 @@ public void scopeValues(ScriptEngine scriptEngine, Map<String, Object> scopeValu
     }
 
     @Override
-    public ScriptEngine createScriptEngine(String scriptType) {
+    public @Nullable ScriptEngine createScriptEngine(String scriptType) {
         return new DebuggingGraalScriptEngine<>(
                 new OpenhabGraalJSScriptEngine(injectionEnabled ? INJECTION_CODE : null, jsScriptServiceUtil));
     }
diff --git a/bundles/org.openhab.automation.jsscripting/src/main/java/org/openhab/automation/jsscripting/internal/OpenhabGraalJSScriptEngine.java b/bundles/org.openhab.automation.jsscripting/src/main/java/org/openhab/automation/jsscripting/internal/OpenhabGraalJSScriptEngine.java
index c4d1037dc97fe..c2e8759bc8611 100644
--- a/bundles/org.openhab.automation.jsscripting/src/main/java/org/openhab/automation/jsscripting/internal/OpenhabGraalJSScriptEngine.java
+++ b/bundles/org.openhab.automation.jsscripting/src/main/java/org/openhab/automation/jsscripting/internal/OpenhabGraalJSScriptEngine.java
@@ -92,7 +92,7 @@ public class OpenhabGraalJSScriptEngine
 
     // these fields start as null because they are populated on first use
     private String engineIdentifier;
-    private Consumer<String> scriptDependencyListener;
+    private @Nullable Consumer<String> scriptDependencyListener;
 
     private boolean initialized = false;
     private final String globalScript;
diff --git a/bundles/org.openhab.automation.jsscripting/src/main/java/org/openhab/automation/jsscripting/internal/scope/AbstractScriptExtensionProvider.java b/bundles/org.openhab.automation.jsscripting/src/main/java/org/openhab/automation/jsscripting/internal/scope/AbstractScriptExtensionProvider.java
index 97520e98cc8c9..04fffeaeb7b10 100644
--- a/bundles/org.openhab.automation.jsscripting/src/main/java/org/openhab/automation/jsscripting/internal/scope/AbstractScriptExtensionProvider.java
+++ b/bundles/org.openhab.automation.jsscripting/src/main/java/org/openhab/automation/jsscripting/internal/scope/AbstractScriptExtensionProvider.java
@@ -13,7 +13,11 @@
 
 package org.openhab.automation.jsscripting.internal.scope;
 
-import java.util.*;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Objects;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.function.Function;
 
@@ -28,7 +32,7 @@
  * @author Jonathan Gilbert - Initial contribution
  */
 public abstract class AbstractScriptExtensionProvider implements ScriptExtensionProvider {
-    private Map<String, Function<String, Object>> types;
+    private Map<String, Function<String, Object>> types = new HashMap<>();
     private Map<String, Map<String, Object>> idToTypes = new ConcurrentHashMap<>();
 
     protected abstract String getPresetName();
@@ -41,7 +45,6 @@ protected void addType(String name, Function<String, Object> value) {
 
     @Activate
     public void activate(final BundleContext context) {
-        types = new HashMap<>();
         initializeTypes(context);
     }
 
diff --git a/bundles/org.openhab.automation.jsscripting/src/main/java/org/openhab/automation/jsscripting/internal/scope/ScriptDisposalAwareScriptExtensionProvider.java b/bundles/org.openhab.automation.jsscripting/src/main/java/org/openhab/automation/jsscripting/internal/scope/ScriptDisposalAwareScriptExtensionProvider.java
index 380f0214d7d89..d8ae613f46700 100644
--- a/bundles/org.openhab.automation.jsscripting/src/main/java/org/openhab/automation/jsscripting/internal/scope/ScriptDisposalAwareScriptExtensionProvider.java
+++ b/bundles/org.openhab.automation.jsscripting/src/main/java/org/openhab/automation/jsscripting/internal/scope/ScriptDisposalAwareScriptExtensionProvider.java
@@ -13,7 +13,11 @@
 
 package org.openhab.automation.jsscripting.internal.scope;
 
-import java.util.*;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Objects;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.function.Function;
 
diff --git a/bundles/org.openhab.automation.jsscripting/src/main/java/org/openhab/automation/jsscripting/internal/scriptengine/DelegatingScriptEngineWithInvocableAndAutocloseable.java b/bundles/org.openhab.automation.jsscripting/src/main/java/org/openhab/automation/jsscripting/internal/scriptengine/DelegatingScriptEngineWithInvocableAndAutocloseable.java
index f96ce621db4d1..182dddb797f5d 100644
--- a/bundles/org.openhab.automation.jsscripting/src/main/java/org/openhab/automation/jsscripting/internal/scriptengine/DelegatingScriptEngineWithInvocableAndAutocloseable.java
+++ b/bundles/org.openhab.automation.jsscripting/src/main/java/org/openhab/automation/jsscripting/internal/scriptengine/DelegatingScriptEngineWithInvocableAndAutocloseable.java
@@ -14,7 +14,6 @@
 package org.openhab.automation.jsscripting.internal.scriptengine;
 
 import java.io.Reader;
-import java.util.Objects;
 
 import javax.script.Bindings;
 import javax.script.Invocable;
@@ -23,7 +22,7 @@
 import javax.script.ScriptEngineFactory;
 import javax.script.ScriptException;
 
-import org.eclipse.jdt.annotation.Nullable;
+import org.eclipse.jdt.annotation.NonNull;
 
 /**
  * {@link ScriptEngine} implementation that delegates to a supplied ScriptEngine instance. Allows overriding specific
@@ -33,94 +32,90 @@
  */
 public abstract class DelegatingScriptEngineWithInvocableAndAutocloseable<T extends ScriptEngine & Invocable & AutoCloseable>
         implements ScriptEngine, Invocable, AutoCloseable {
-    protected T delegate;
+    protected @NonNull T delegate;
 
-    public DelegatingScriptEngineWithInvocableAndAutocloseable(T delegate) {
+    public DelegatingScriptEngineWithInvocableAndAutocloseable(@NonNull T delegate) {
         this.delegate = delegate;
     }
 
     @Override
-    public @Nullable Object eval(String s, ScriptContext scriptContext) throws ScriptException {
-        return Objects.nonNull(delegate) ? delegate.eval(s, scriptContext) : null;
+    public Object eval(String s, ScriptContext scriptContext) throws ScriptException {
+        return delegate.eval(s, scriptContext);
     }
 
     @Override
-    public @Nullable Object eval(Reader reader, ScriptContext scriptContext) throws ScriptException {
-        return Objects.nonNull(delegate) ? delegate.eval(reader, scriptContext) : null;
+    public Object eval(Reader reader, ScriptContext scriptContext) throws ScriptException {
+        return delegate.eval(reader, scriptContext);
     }
 
     @Override
-    public @Nullable Object eval(String s) throws ScriptException {
-        return Objects.nonNull(delegate) ? delegate.eval(s) : null;
+    public Object eval(String s) throws ScriptException {
+        return delegate.eval(s);
     }
 
     @Override
-    public @Nullable Object eval(Reader reader) throws ScriptException {
-        return Objects.nonNull(delegate) ? delegate.eval(reader) : null;
+    public Object eval(Reader reader) throws ScriptException {
+        return delegate.eval(reader);
     }
 
     @Override
-    public @Nullable Object eval(String s, Bindings bindings) throws ScriptException {
-        return Objects.nonNull(delegate) ? delegate.eval(s, bindings) : null;
+    public Object eval(String s, Bindings bindings) throws ScriptException {
+        return delegate.eval(s, bindings);
     }
 
     @Override
-    public @Nullable Object eval(Reader reader, Bindings bindings) throws ScriptException {
-        return Objects.nonNull(delegate) ? delegate.eval(reader, bindings) : null;
+    public Object eval(Reader reader, Bindings bindings) throws ScriptException {
+        return delegate.eval(reader, bindings);
     }
 
     @Override
     public void put(String s, Object o) {
-        if (Objects.nonNull(delegate))
-            delegate.put(s, o);
+        delegate.put(s, o);
     }
 
     @Override
-    public @Nullable Object get(String s) {
-        return Objects.nonNull(delegate) ? delegate.get(s) : null;
+    public Object get(String s) {
+        return delegate.get(s);
     }
 
     @Override
-    public @Nullable Bindings getBindings(int i) {
-        return Objects.nonNull(delegate) ? delegate.getBindings(i) : null;
+    public Bindings getBindings(int i) {
+        return delegate.getBindings(i);
     }
 
     @Override
     public void setBindings(Bindings bindings, int i) {
-        if (Objects.nonNull(delegate))
-            delegate.setBindings(bindings, i);
+        delegate.setBindings(bindings, i);
     }
 
     @Override
-    public @Nullable Bindings createBindings() {
-        return Objects.nonNull(delegate) ? delegate.createBindings() : null;
+    public Bindings createBindings() {
+        return delegate.createBindings();
     }
 
     @Override
-    public @Nullable ScriptContext getContext() {
-        return Objects.nonNull(delegate) ? delegate.getContext() : null;
+    public ScriptContext getContext() {
+        return delegate.getContext();
     }
 
     @Override
     public void setContext(ScriptContext scriptContext) {
-        if (Objects.nonNull(delegate))
-            delegate.setContext(scriptContext);
+        delegate.setContext(scriptContext);
     }
 
     @Override
-    public @Nullable ScriptEngineFactory getFactory() {
-        return Objects.nonNull(delegate) ? delegate.getFactory() : null;
+    public ScriptEngineFactory getFactory() {
+        return delegate.getFactory();
     }
 
     @Override
-    public @Nullable Object invokeMethod(Object o, String s, Object... objects)
-            throws ScriptException, NoSuchMethodException {
-        return Objects.nonNull(delegate) ? delegate.invokeMethod(o, s, objects) : null;
+    public Object invokeMethod(Object o, String s, Object... objects) throws ScriptException, NoSuchMethodException {
+        return delegate.invokeMethod(o, s, objects);
     }
 
     @Override
-    public @Nullable Object invokeFunction(String s, Object... objects) throws ScriptException, NoSuchMethodException {
-        return Objects.nonNull(delegate) ? delegate.invokeFunction(s, objects) : null;
+    public Object invokeFunction(String s, Object... objects) throws ScriptException, NoSuchMethodException {
+        return delegate.invokeFunction(s, objects);
     }
 
     @Override
@@ -135,7 +130,6 @@ public <T> T getInterface(Object o, Class<T> aClass) {
 
     @Override
     public void close() throws Exception {
-        if (Objects.nonNull(delegate))
-            delegate.close();
+        delegate.close();
     }
 }
diff --git a/bundles/org.openhab.automation.jsscripting/src/main/java/org/openhab/automation/jsscripting/internal/threading/ThreadsafeTimers.java b/bundles/org.openhab.automation.jsscripting/src/main/java/org/openhab/automation/jsscripting/internal/threading/ThreadsafeTimers.java
index c5762217c4b4e..93ce7ca44aac1 100644
--- a/bundles/org.openhab.automation.jsscripting/src/main/java/org/openhab/automation/jsscripting/internal/threading/ThreadsafeTimers.java
+++ b/bundles/org.openhab.automation.jsscripting/src/main/java/org/openhab/automation/jsscripting/internal/threading/ThreadsafeTimers.java
@@ -113,7 +113,7 @@ public long setTimeout(Runnable callback, Long delay) {
      * @return Positive integer value which identifies the timer created; this value can be passed to
      *         <code>clearTimeout()</code> to cancel the timeout.
      */
-    public long setTimeout(Runnable callback, Long delay, Object... args) {
+    public long setTimeout(Runnable callback, Long delay, @Nullable Object... args) {
         long id = lastId.incrementAndGet();
         ScheduledCompletableFuture<Object> future = scheduler.schedule(() -> {
             try {
@@ -166,7 +166,7 @@ public long setInterval(Runnable callback, Long delay) {
      * @return Numeric, non-zero value which identifies the timer created; this value can be passed to
      *         <code>clearInterval()</code> to cancel the interval.
      */
-    public long setInterval(Runnable callback, Long delay, Object... args) {
+    public long setInterval(Runnable callback, Long delay, @Nullable Object... args) {
         long id = lastId.incrementAndGet();
         ScheduledCompletableFuture<Object> future = scheduler.schedule(() -> {
             try {