diff --git a/CHANGELOG.md b/CHANGELOG.md
index 84f4af6..adc4cc7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 -
 
+## [0.2.3] - 2023-05-12
+
+### Added in 0.2.3
+
+- Fix bug (nil observer)
+
 ## [0.2.2] - 2023-05-10
 
 ### Added in 0.2.2
diff --git a/subject/subject_impl.go b/subject/subject_impl.go
index 35c138e..2478540 100644
--- a/subject/subject_impl.go
+++ b/subject/subject_impl.go
@@ -103,10 +103,12 @@ Input
 */
 func (subject *SubjectImpl) RegisterObserver(ctx context.Context, observer observer.Observer) error {
 	var err error = nil
-	lock.RLock()
-	defer lock.RUnlock()
-	if !contains(ctx, subject.observerList, observer) {
-		subject.observerList = append(subject.observerList, observer)
+	if observer != nil {
+		lock.RLock()
+		defer lock.RUnlock()
+		if !contains(ctx, subject.observerList, observer) {
+			subject.observerList = append(subject.observerList, observer)
+		}
 	}
 	return err
 }
@@ -121,8 +123,10 @@ Input
 */
 func (subject *SubjectImpl) UnregisterObserver(ctx context.Context, observer observer.Observer) error {
 	var err error = nil
-	lock.RLock()
-	defer lock.RUnlock()
-	subject.observerList = removeFromSlice(ctx, subject.observerList, observer)
+	if observer != nil {
+		lock.RLock()
+		defer lock.RUnlock()
+		subject.observerList = removeFromSlice(ctx, subject.observerList, observer)
+	}
 	return err
 }