chore: address comment

Author: maxakuru

src/templates/json/JSONTemplate.js

@@ -74,7 +74,7 @@ export class JSONTemplate {
   constructMPN(variant) {
     return variant
       ? variant.attributes.find((attr) => attr.name.toLowerCase() === 'mpn')?.value ?? this.constructMPN()
-      : this.product.attributes.find((attr) => attr.name.toLowerCase() === 'mpn')?.value ?? this.product.sku;
+      : this.product.attributes.find((attr) => attr.name.toLowerCase() === 'mpn')?.value ?? undefined;
   }
 
   renderBrand() {

src/templates/json/overrides/wilson-ecommerce--wilson.js

@@ -24,4 +24,11 @@ export default class extends JSONTemplate {
       },
     };
   }
+
+  /**
+   * @param {Variant} [variant]
+   */
+  constructMPN(variant) {
+    return variant ? variant.sku : this.product.sku;
+  }
 }