1 files changed, 4 insertions, 2 deletions
diff --git a/Timeline/Services/DatabaseExtensions.cs b/Timeline/Services/DatabaseExtensions.cs
index 8cbc8fef..140c3146 100644
--- a/Timeline/Services/DatabaseExtensions.cs
+++ b/Timeline/Services/DatabaseExtensions.cs
@@ -9,6 +9,8 @@ namespace Timeline.Services
 {
     internal static class DatabaseExtensions
     {
+        private static readonly UsernameValidator usernameValidator = new UsernameValidator();
+
         /// <summary>
         /// Check the existence and get the id of the user.
         /// </summary>
@@ -17,11 +19,11 @@ namespace Timeline.Services
         /// <exception cref="ArgumentNullException">Thrown if <paramref name="username"/> is null.</exception>
         /// <exception cref="UsernameBadFormatException">Thrown if <paramref name="username"/> is of bad format.</exception>
         /// <exception cref="UserNotExistException">Thrown if user does not exist.</exception>
-        internal static async Task<long> CheckAndGetUser(DbSet<User> userDbSet, UsernameValidator validator, string username)
+        internal static async Task<long> CheckAndGetUser(DbSet<User> userDbSet, string? username)
         {
             if (username == null)
                 throw new ArgumentNullException(nameof(username));
-            var (result, message) = validator.Validate(username);
+            var (result, message) = usernameValidator.Validate(username);
             if (!result)
                 throw new UsernameBadFormatException(username, message);