diff --git a/pom.xml b/pom.xml
index f6b039f..5f6877d 100644
--- a/pom.xml
+++ b/pom.xml
@@ -6,7 +6,7 @@
     <parent>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-parent</artifactId>
-        <version>3.3.2</version>
+        <version>3.3.4</version>
         <relativePath/> <!-- lookup parent from repository -->
     </parent>
 
diff --git a/src/main/java/it/aboutbits/springboot/testing/testdata/base/ModifyableTestDataCreator.java b/src/main/java/it/aboutbits/springboot/testing/testdata/base/ModifyableTestDataCreator.java
index bd12e1c..4d28cd1 100644
--- a/src/main/java/it/aboutbits/springboot/testing/testdata/base/ModifyableTestDataCreator.java
+++ b/src/main/java/it/aboutbits/springboot/testing/testdata/base/ModifyableTestDataCreator.java
@@ -2,6 +2,7 @@
 
 import it.aboutbits.springboot.testing.spring.BeanAccessor;
 import jakarta.persistence.EntityManager;
+import lombok.NonNull;
 import lombok.extern.slf4j.Slf4j;
 import org.springframework.transaction.support.TransactionTemplate;
 
@@ -29,7 +30,7 @@ protected ModifyableTestDataCreator(int count) {
         super(count);
     }
 
-    public CREATOR modifyParameter(BiFunction<PARAMETER, Integer, PARAMETER> parameterMutator) {
+    public CREATOR modifyParameter(@NonNull BiFunction<PARAMETER, Integer, PARAMETER> parameterMutator) {
         this.parameterMutator = (parameter, index) -> {
             mutatorCalled = true;
             return parameterMutator.apply(parameter, index);
@@ -38,7 +39,7 @@ public CREATOR modifyParameter(BiFunction<PARAMETER, Integer, PARAMETER> paramet
         return (CREATOR) this;
     }
 
-    public CREATOR modifyParameter(UnaryOperator<PARAMETER> parameterMutator) {
+    public CREATOR modifyParameter(@NonNull UnaryOperator<PARAMETER> parameterMutator) {
         this.parameterMutator = (parameter, index) -> {
             mutatorCalled = true;
             return parameterMutator.apply(parameter);
@@ -47,12 +48,12 @@ public CREATOR modifyParameter(UnaryOperator<PARAMETER> parameterMutator) {
         return (CREATOR) this;
     }
 
-    public CREATOR modifyResult(ObjIntConsumer<ITEM> resultMutator) {
+    public CREATOR modifyResult(@NonNull ObjIntConsumer<ITEM> resultMutator) {
         this.resultMutator = resultMutator;
         return (CREATOR) this;
     }
 
-    public CREATOR modifyResult(Consumer<ITEM> resultMutator) {
+    public CREATOR modifyResult(@NonNull Consumer<ITEM> resultMutator) {
         this.resultMutator = (item, index) -> resultMutator.accept(item);
         return (CREATOR) this;
     }
@@ -79,7 +80,7 @@ protected List<ITEM> create() {
         return result;
     }
 
-    protected ITEM saveMutation(ITEM item) {
+    protected ITEM saveMutation(@NonNull ITEM item) {
         var entityManager = BeanAccessor.getBean(EntityManager.class);
         var transactionTemplate = BeanAccessor.getBean(TransactionTemplate.class);
 
diff --git a/src/main/java/it/aboutbits/springboot/testing/testdata/base/TestDataCreator.java b/src/main/java/it/aboutbits/springboot/testing/testdata/base/TestDataCreator.java
index 3a23885..25f2fb6 100644
--- a/src/main/java/it/aboutbits/springboot/testing/testdata/base/TestDataCreator.java
+++ b/src/main/java/it/aboutbits/springboot/testing/testdata/base/TestDataCreator.java
@@ -1,5 +1,7 @@
 package it.aboutbits.springboot.testing.testdata.base;
 
+import lombok.NonNull;
+
 import java.util.ArrayList;
 import java.util.Comparator;
 import java.util.HashSet;
@@ -26,11 +28,11 @@ public List<ITEM> returnAll() {
         return create();
     }
 
-    public List<ITEM> returnSorted(Comparator<ITEM> comparator) {
+    public List<ITEM> returnSorted(@NonNull Comparator<ITEM> comparator) {
         return returnAll().stream().sorted(comparator).toList();
     }
 
-    public <U extends Comparable<? super U>> List<ITEM> returnSorted(Function<ITEM, U> comparator) {
+    public <U extends Comparable<? super U>> List<ITEM> returnSorted(@NonNull Function<ITEM, U> comparator) {
         return returnAll().stream()
                 .sorted(Comparator.comparing(comparator))
                 .toList();