Clean up

src/Imprink.Application/ProductVariants/Validation/GetProductVariantsQueryValidator.cs

@@ -0,0 +1,14 @@
+using FluentValidation;
+using Imprink.Application.Domains.ProductVariants;
+
+namespace Imprink.Application.Validation.ProductVariants;
+
+public class GetProductVariantsQueryValidator : AbstractValidator<GetProductVariantsQuery>
+{
+    public GetProductVariantsQueryValidator()
+    {
+        RuleFor(x => x.ProductId)
+            .NotEqual(Guid.Empty).When(x => x.ProductId.HasValue)
+            .WithMessage("ProductId must be a valid GUID when provided.");
+    }
+}