fix: preserve empty arrays in facet fields

Change truthy checks to explicit !== undefined checks for
shortDescriptionFacets and descriptionFacets to ensure empty
arrays are preserved as valid values.

Fixes unresolved comment from PR #112 review thread #3700691486

Author: aspiers

packages/sdk-core/src/repository/HypercertOperationsImpl.ts

@@ -283,11 +283,11 @@ export class HypercertOperationsImpl extends EventEmitter<HypercertEvents> imple
       hypercertRecord.image = imageBlobRef;
     }
 
-    if (params.shortDescriptionFacets) {
+    if (params.shortDescriptionFacets !== undefined) {
       hypercertRecord.shortDescriptionFacets = params.shortDescriptionFacets;
     }
 
-    if (params.descriptionFacets) {
+    if (params.descriptionFacets !== undefined) {
       hypercertRecord.descriptionFacets = params.descriptionFacets;
     }