diff --git a/src/main/java/org/gelecekbilimde/scienceplatform/common/util/validation/UsernameValidator.java b/src/main/java/org/gelecekbilimde/scienceplatform/common/util/validation/UsernameValidator.java
index ecb1c7c..8132071 100644
--- a/src/main/java/org/gelecekbilimde/scienceplatform/common/util/validation/UsernameValidator.java
+++ b/src/main/java/org/gelecekbilimde/scienceplatform/common/util/validation/UsernameValidator.java
@@ -16,7 +16,7 @@ public boolean isValid(String value, ConstraintValidatorContext context) {
 
 		String lowerCasedValue = value.toLowerCase();
 
-		if (value.startsWith(" ") || value.endsWith(" ")) {
+		if (!value.trim().equals(value)) {
 			context.disableDefaultConstraintViolation();
 			context.buildConstraintViolationWithTemplate("name must not start or end with whitespace")
 				.addConstraintViolation();
diff --git a/src/main/java/org/gelecekbilimde/scienceplatform/user/exception/UsernameAlreadyTakenException.java b/src/main/java/org/gelecekbilimde/scienceplatform/user/exception/UsernameAlreadyTakenException.java
index a8fea78..1f243c0 100644
--- a/src/main/java/org/gelecekbilimde/scienceplatform/user/exception/UsernameAlreadyTakenException.java
+++ b/src/main/java/org/gelecekbilimde/scienceplatform/user/exception/UsernameAlreadyTakenException.java
@@ -1,16 +1,16 @@
 package org.gelecekbilimde.scienceplatform.user.exception;
 
-import org.gelecekbilimde.scienceplatform.common.exception.AbstractServerException;
+import org.gelecekbilimde.scienceplatform.common.exception.AbstractConflictException;
 
 import java.io.Serial;
 
-public final class UsernameAlreadyTakenException extends AbstractServerException {
+public final class UsernameAlreadyTakenException extends AbstractConflictException {
 
 	@Serial
 	private static final long serialVersionUID = -3365493595680402581L;
 
 	public UsernameAlreadyTakenException(String username) {
-		super(("username is already taken" + username));
+		super(String.format("'%s' username already taken", username));
 	}
 
 }
diff --git a/src/main/java/org/gelecekbilimde/scienceplatform/user/model/User.java b/src/main/java/org/gelecekbilimde/scienceplatform/user/model/User.java
index 2ef1c87..deb1e1a 100644
--- a/src/main/java/org/gelecekbilimde/scienceplatform/user/model/User.java
+++ b/src/main/java/org/gelecekbilimde/scienceplatform/user/model/User.java
@@ -34,7 +34,7 @@ public class User extends BaseDomainModel {
 
 
 	public String getUsername() {
-		return username.toLowerCase();
+		return username != null ? username.toLowerCase() : null;
 	}