diff --git a/api/src/main/java/io/cloudevents/rw/CloudEventAttributesWriter.java b/api/src/main/java/io/cloudevents/rw/CloudEventAttributesWriter.java
index 899988dd..84d66fbb 100644
--- a/api/src/main/java/io/cloudevents/rw/CloudEventAttributesWriter.java
+++ b/api/src/main/java/io/cloudevents/rw/CloudEventAttributesWriter.java
@@ -17,7 +17,6 @@
 
 package io.cloudevents.rw;
 
-import io.cloudevents.lang.Nullable;
 import io.cloudevents.types.Time;
 
 import java.net.URI;
@@ -37,29 +36,29 @@ public interface CloudEventAttributesWriter {
      * @return self
      * @throws CloudEventRWException if anything goes wrong while writing this attribute.
      */
-    CloudEventAttributesWriter withAttribute(String name, @Nullable String value) throws CloudEventRWException;
+    CloudEventAttributesWriter withAttribute(String name, String value) throws CloudEventRWException;
 
     /**
      * Set attribute with type {@link URI}.
      *
-     * @param name name of the attribute
+     * @param name  name of the attribute
      * @param value value of the attribute
-     * @throws CloudEventRWException if anything goes wrong while writing this attribute.
      * @return self
+     * @throws CloudEventRWException if anything goes wrong while writing this attribute.
      */
-    default CloudEventAttributesWriter withAttribute(String name, @Nullable URI value) throws CloudEventRWException {
+    default CloudEventAttributesWriter withAttribute(String name, URI value) throws CloudEventRWException {
         return withAttribute(name, value == null ? null : value.toString());
     }
 
     /**
      * Set attribute with type {@link OffsetDateTime} attribute.
      *
-     * @param name name of the attribute
+     * @param name  name of the attribute
      * @param value value of the attribute
-     * @throws CloudEventRWException if anything goes wrong while writing this attribute.
      * @return self
+     * @throws CloudEventRWException if anything goes wrong while writing this attribute.
      */
-    default CloudEventAttributesWriter withAttribute(String name, @Nullable OffsetDateTime value) throws CloudEventRWException {
+    default CloudEventAttributesWriter withAttribute(String name, OffsetDateTime value) throws CloudEventRWException {
         return withAttribute(name, value == null ? null : Time.writeTime(name, value));
     }
 
diff --git a/api/src/main/java/io/cloudevents/rw/CloudEventExtensionsWriter.java b/api/src/main/java/io/cloudevents/rw/CloudEventExtensionsWriter.java
index d6c39157..155718e1 100644
--- a/api/src/main/java/io/cloudevents/rw/CloudEventExtensionsWriter.java
+++ b/api/src/main/java/io/cloudevents/rw/CloudEventExtensionsWriter.java
@@ -17,8 +17,6 @@
 
 package io.cloudevents.rw;
 
-import io.cloudevents.lang.Nullable;
-
 import java.net.URI;
 
 /**
@@ -34,29 +32,29 @@ public interface CloudEventExtensionsWriter {
      * @return self
      * @throws CloudEventRWException if anything goes wrong while writing this extension.
      */
-    CloudEventExtensionsWriter withExtension(String name, @Nullable String value) throws CloudEventRWException;
+    CloudEventExtensionsWriter withExtension(String name, String value) throws CloudEventRWException;
 
     /**
      * Set attribute with type {@link URI}.
      *
-     * @param name name of the extension
+     * @param name  name of the extension
      * @param value value of the extension
-     * @throws CloudEventRWException if anything goes wrong while writing this extension.
      * @return self
+     * @throws CloudEventRWException if anything goes wrong while writing this extension.
      */
-    default CloudEventExtensionsWriter withExtension(String name, @Nullable Number value) throws CloudEventRWException {
+    default CloudEventExtensionsWriter withExtension(String name, Number value) throws CloudEventRWException {
         return withExtension(name, value == null ? null : value.toString());
     }
 
     /**
      * Set attribute with type {@link Boolean} attribute.
      *
-     * @param name name of the extension
+     * @param name  name of the extension
      * @param value value of the extension
-     * @throws CloudEventRWException if anything goes wrong while writing this extension.
      * @return self
+     * @throws CloudEventRWException if anything goes wrong while writing this extension.
      */
-    default CloudEventExtensionsWriter withExtension(String name, @Nullable Boolean value) throws CloudEventRWException {
+    default CloudEventExtensionsWriter withExtension(String name, Boolean value) throws CloudEventRWException {
         return withExtension(name, value == null ? null : value.toString());
     }
 
diff --git a/core/src/main/java/io/cloudevents/core/builder/CloudEventBuilder.java b/core/src/main/java/io/cloudevents/core/builder/CloudEventBuilder.java
index 8cdc34c6..49203c6b 100644
--- a/core/src/main/java/io/cloudevents/core/builder/CloudEventBuilder.java
+++ b/core/src/main/java/io/cloudevents/core/builder/CloudEventBuilder.java
@@ -152,7 +152,7 @@ public interface CloudEventBuilder extends CloudEventWriter<CloudEvent> {
      * @return self
      */
     @Override
-    CloudEventBuilder withExtension(@Nonnull String key, String value);
+    CloudEventBuilder withExtension(@Nonnull String key, @Nonnull String value);
 
     /**
      * Set an extension with provided key and numeric value
@@ -162,7 +162,7 @@ public interface CloudEventBuilder extends CloudEventWriter<CloudEvent> {
      * @return self
      */
     @Override
-    CloudEventBuilder withExtension(@Nonnull String key, Number value);
+    CloudEventBuilder withExtension(@Nonnull String key, @Nonnull Number value);
 
     /**
      * Set an extension with provided key and boolean value
@@ -172,7 +172,7 @@ public interface CloudEventBuilder extends CloudEventWriter<CloudEvent> {
      * @return self
      */
     @Override
-    CloudEventBuilder withExtension(@Nonnull String key, Boolean value);
+    CloudEventBuilder withExtension(@Nonnull String key, @Nonnull Boolean value);
 
     /**
      * Add to the builder all the extension key/values of the provided extension
diff --git a/core/src/main/java/io/cloudevents/core/impl/BaseCloudEventBuilder.java b/core/src/main/java/io/cloudevents/core/impl/BaseCloudEventBuilder.java
index 7e1b5915..96a41c42 100644
--- a/core/src/main/java/io/cloudevents/core/impl/BaseCloudEventBuilder.java
+++ b/core/src/main/java/io/cloudevents/core/impl/BaseCloudEventBuilder.java
@@ -96,24 +96,24 @@ public abstract class BaseCloudEventBuilder<SELF extends BaseCloudEventBuilder<S
         return this.self;
     }
 
-    public SELF withExtension(@Nonnull String key, String value) {
-        if(!isValidExtensionName(key)){
+    public SELF withExtension(@Nonnull String key, @Nonnull String value) {
+        if (!isValidExtensionName(key)) {
             throw CloudEventRWException.newInvalidExtensionName(key);
         }
         this.extensions.put(key, value);
         return self;
     }
 
-    public SELF withExtension(@Nonnull String key, Number value) {
-        if(!isValidExtensionName(key)){
+    public SELF withExtension(@Nonnull String key, @Nonnull Number value) {
+        if (!isValidExtensionName(key)) {
             throw CloudEventRWException.newInvalidExtensionName(key);
         }
         this.extensions.put(key, value);
         return self;
     }
 
-    public SELF withExtension(@Nonnull String key, Boolean value) {
-        if(!isValidExtensionName(key)){
+    public SELF withExtension(@Nonnull String key, @Nonnull Boolean value) {
+        if (!isValidExtensionName(key)) {
             throw CloudEventRWException.newInvalidExtensionName(key);
         }
         this.extensions.put(key, value);