diff --git a/core-java-8/src/main/java/com/baeldung/customannotations/ObjectToJsonConverter.java b/core-java-8/src/main/java/com/baeldung/customannotations/ObjectToJsonConverter.java
index bcde225a3b..dd126be8ed 100644
--- a/core-java-8/src/main/java/com/baeldung/customannotations/ObjectToJsonConverter.java
+++ b/core-java-8/src/main/java/com/baeldung/customannotations/ObjectToJsonConverter.java
@@ -8,10 +8,8 @@ import java.util.Map;
 import java.util.Objects;
 import java.util.stream.Collectors;
 
-import com.sun.istack.internal.NotNull;
-
 public class ObjectToJsonConverter {
-    public String convertToJson(@NotNull Object object) throws JsonSerializationException {
+    public String convertToJson(Object object) throws JsonSerializationException {
         try {
 
             checkIfSerializable(object);
@@ -30,7 +28,7 @@ public class ObjectToJsonConverter {
 
         Class<?> clazz = object.getClass();
         if (!clazz.isAnnotationPresent(JsonSerializable.class)) {
-            throw new JsonSerializationException("The class" + clazz.getSimpleName() + " is not annotated with JsonSerializable");
+            throw new JsonSerializationException("The class " + clazz.getSimpleName() + " is not annotated with JsonSerializable");
         }
     }