Fix flash sales cache invalidators

plugins/FlashSales/src/EasyAbp.EShop.Plugins.FlashSales.Application/EasyAbp/EShop/Plugins/FlashSales/FlashSalePlans/FlashSalePlanCacheInvalidator.cs

@@ -25,7 +25,7 @@ public class FlashSalePlanCacheInvalidator : ILocalEventHandler<EntityChangedEve
     {
         await DistributedCache.RemoveAsync(eventData.Entity.Id);
 
-        UnitOfWorkManager.Current.OnCompleted(async () =>
+        UnitOfWorkManager.Current?.OnCompleted(async () =>
         {
             await DistributedCache.RemoveAsync(eventData.Entity.Id);
         });

plugins/FlashSales/src/EasyAbp.EShop.Plugins.FlashSales.Application/EasyAbp/EShop/Products/Products/ProductCacheInvalidator.cs

@@ -28,7 +28,7 @@ public class ProductCacheInvalidator :
     {
         await DistributedCache.RemoveAsync(eventData.Entity.Id);
 
-        UnitOfWorkManager.Current.OnCompleted(async () =>
+        UnitOfWorkManager.Current?.OnCompleted(async () =>
         {
             await DistributedCache.RemoveAsync(eventData.Entity.Id);
         });
@@ -38,7 +38,7 @@ public class ProductCacheInvalidator :
     {
         await DistributedCache.RemoveAsync(eventData.Entity.Id);
 
-        UnitOfWorkManager.Current.OnCompleted(async () =>
+        UnitOfWorkManager.Current?.OnCompleted(async () =>
         {
             await DistributedCache.RemoveAsync(eventData.Entity.Id);
         });