fix(classes.collection): Guard against missing collection before attaching document constructor in Collection decorator

ts/classes.collection.ts

@@ -41,7 +41,7 @@ export function Collection(dbArg: SmartdataDb | TDelayed<SmartdataDb>) {
       }
       const coll = collectionFactory.getCollection(constructor.name, dbArg);
       // Attach document constructor for searchableFields lookup
-      if (!(coll as any).docCtor) {
+      if (coll && !(coll as any).docCtor) {
         (coll as any).docCtor = decoratedClass;
       }
       return coll;