diff --git a/API_SQLuedo/API/Controllers/UsersController.cs b/API_SQLuedo/API/Controllers/UsersController.cs
index 13812b4..dc270d2 100644
--- a/API_SQLuedo/API/Controllers/UsersController.cs
+++ b/API_SQLuedo/API/Controllers/UsersController.cs
@@ -91,9 +91,17 @@ namespace API.Controllers
             {
                 return BadRequest();
             }
+            try
+            {
+                _logger.LogInformation("[INFORMATION] Un utilisateur a été créé : username - {username}, password - {password}, email - {email}, isAdmin - {isAdmin}", dto.Username, dto.Password, dto.Email, dto.IsAdmin);
+                var user = await _dataService.UserService.AddItem(dto);
+                return Created(nameof(GetUsers), user);
+            }
+            catch (InvalidOperationException)
+            {
+                return StatusCode(409);
+            }
 
-            _logger.LogInformation("[INFORMATION] Un utilisateur a été créé : username - {username}, password - {password}, email - {email}, isAdmin - {isAdmin}", dto.Username, dto.Password, dto.Email, dto.IsAdmin);
-            return Created(nameof(GetUsers), _dataService.UserService.AddItem(dto));
         }
 
         [HttpPut]
diff --git a/API_SQLuedo/ModelToEntity/DbDataManager.cs b/API_SQLuedo/ModelToEntity/DbDataManager.cs
index b82de68..c571461 100644
--- a/API_SQLuedo/ModelToEntity/DbDataManager.cs
+++ b/API_SQLuedo/ModelToEntity/DbDataManager.cs
@@ -165,7 +165,12 @@ namespace ModelToEntity
         {
             using (var context = new UserDbContext())
             {
-                return (await context.CreateItemAsync(item.FromModelToEntity())).FromEntityToModel() ;
+                var user = await context.CreateItemAsync(item.FromModelToEntity());
+                if (user == null)
+                {
+                    return null;
+                }
+                return user.FromEntityToModel() ;
             }
         }
 
diff --git a/API_SQLuedo/ModelToEntity/Extension.cs b/API_SQLuedo/ModelToEntity/Extension.cs
index b1ea30d..3cc95d0 100644
--- a/API_SQLuedo/ModelToEntity/Extension.cs
+++ b/API_SQLuedo/ModelToEntity/Extension.cs
@@ -21,7 +21,7 @@ namespace ModelToEntity
         {
             if (item == null || context.Set<T>().Contains(item))
             {
-                return Task.FromResult<T?>(default(T));
+                return Task.FromResult<T?>(null);
             }
 
             context.Set<T>().Add(item);
diff --git a/API_SQLuedo/Services/UserDataService.cs b/API_SQLuedo/Services/UserDataService.cs
index 6a0f952..4ace5ec 100644
--- a/API_SQLuedo/Services/UserDataService.cs
+++ b/API_SQLuedo/Services/UserDataService.cs
@@ -59,6 +59,10 @@ namespace Services
         public async Task<UserDTO?> AddItem(UserDTO? item)
         {
             var newItem = await dataServiceEF.AddItem(item.FromDTOToModel());
+            if (newItem == null) 
+            {
+                throw new InvalidOperationException();
+            }
             return newItem.FromModelToDTO();
         }