Add missed non-nullables to XDigitalCatalog

src/VirtoCommerce.ExperienceApiModule.DigitalCatalog/Queries/ChildCategoriesQueryHandler.cs

@@ -54,7 +54,7 @@ public virtual async Task<ChildCategoriesQueryResponse> Handle(ChildCategoriesQu
             level--;
         }
 
-        result.ChildCategories = root.ChildCategories ?? new List<ExpCategory>();
+        result.ChildCategories = root.ChildCategories;
 
         // try resolve products via facets
         if (!string.IsNullOrEmpty(request.ProductFilter))

src/VirtoCommerce.ExperienceApiModule.DigitalCatalog/Queries/ChildCategoriesQueryResponse.cs

@@ -4,5 +4,5 @@ namespace VirtoCommerce.XDigitalCatalog.Queries;
 
 public class ChildCategoriesQueryResponse
 {
-    public IList<ExpCategory> ChildCategories { get; set; }
+    public IList<ExpCategory> ChildCategories { get; set; } = new List<ExpCategory>();
 }

src/VirtoCommerce.ExperienceApiModule.DigitalCatalog/Queries/ChildCategoriesQueryResponseType.cs

@@ -8,7 +8,7 @@ public class ChildCategoriesQueryResponseType : ExtendableGraphType<ChildCategor
 {
     public ChildCategoriesQueryResponseType()
     {
-        Field<ListGraphType<CategoryType>>(
+        Field<NonNullGraphType<ListGraphType<NonNullGraphType<CategoryType>>>>(
             nameof(ChildCategoriesQueryResponse.ChildCategories),
             resolve: context => context.Source.ChildCategories);
     }

src/VirtoCommerce.ExperienceApiModule.DigitalCatalog/Queries/ProductSuggestionsQueryResponseType.cs

@@ -7,7 +7,7 @@ public class ProductSuggestionsQueryResponseType : ExtendableGraphType<ProductSu
 {
     public ProductSuggestionsQueryResponseType()
     {
-        Field<ListGraphType<StringGraphType>>(
+        Field<NonNullGraphType<ListGraphType<NonNullGraphType<StringGraphType>>>>(
             nameof(ProductSuggestionsQueryResponse.Suggestions),
             resolve: context => context.Source.Suggestions);
     }

src/XPurchase/VirtoCommerce.XPurchase/Schemas/PurchaseSchema.cs

@@ -840,7 +840,7 @@ public void Build(ISchema schema)
             ///   }
             /// }
             /// </example>
-            var validateCouponField = FieldBuilder.Create<CartAggregate, bool>(typeof(BooleanGraphType))
+            var validateCouponField = FieldBuilder.Create<CartAggregate, bool>(typeof(NonNullGraphType<BooleanGraphType>))
                                                   .Name("validateCoupon")
                                                   .Argument(GraphTypeExtenstionHelper.GetActualComplexType<NonNullGraphType<InputValidateCouponType>>(), _commandName)
                                                   .ResolveSynchronizedAsync(CartPrefix, "userId", _distributedLockService, async context =>