Put input validation before field assignment

src/main/java/model/User.java

@@ -9,11 +9,6 @@ public class User {
   private final PasswordHash password;
 
   public User(String userName, String phoneNumber, PasswordHash password, String eMail) {
-    this.userName = userName;
-    this.phoneNumber = phoneNumber;
-    this.eMail = eMail;
-    this.password = password;
-
     if ( userName == null || userName.isBlank() ) {
       throw new IllegalArgumentException("Username has to be filled in");
     }
@@ -23,12 +18,17 @@ public User(String userName, String phoneNumber, PasswordHash password, String e
     }
 
     if ( phoneNumber == null || phoneNumber.isBlank() ) {
-      throw new IllegalArgumentException("Phonenumber has to be filled in");
+      throw new IllegalArgumentException("Phone number has to be filled in");
     }
 
     if ( phoneNumber.length() != 8 ) {
-      throw new IllegalArgumentException("Fill in a phonenumber with 8 digits");
+      throw new IllegalArgumentException("Fill in a phone number with 8 digits");
     }
+
+    this.userName = userName;
+    this.phoneNumber = phoneNumber;
+    this.eMail = eMail;
+    this.password = password;
   }
 
   public String getUsername() { return userName; }