Add test

colaflow-api/src/Modules/Identity/ColaFlow.Modules.Identity.Application/Commands/Login/LoginCommandHandler.cs

@@ -35,7 +35,7 @@ public class LoginCommandHandler(
         }
 
         // 3. Verify password
-        if (user.PasswordHash == null || !passwordHasher.VerifyPassword(request.Password, user.PasswordHash))
+        if (string.IsNullOrEmpty(user.PasswordHash) || !passwordHasher.VerifyPassword(request.Password, user.PasswordHash))
         {
             throw new UnauthorizedAccessException("Invalid credentials");
         }
@@ -46,7 +46,7 @@ public class LoginCommandHandler(
             tenant.Id,
             cancellationToken);
 
-        if (userTenantRole == null)
+        if (userTenantRole is null)
         {
             throw new InvalidOperationException($"User {user.Id} has no role assigned for tenant {tenant.Id}");
         }