Fix mongo query for null value

Due to an optimistic type change earlier in the upgrade it was
possible here to send through an empty string which angers Mongo.
Since we've typed the var strictly to a string we can check here
for an empty string explicitly.

app/api/blueprint-controller.ts

@@ -292,8 +292,8 @@ export class BlueprintController {
 
       let filter: any = { $and: [{ createdAt: { $lt: dateFilter } }, { deleted: { $ne: true } }] };
 
-      if (filterUserId != null) filter.$and.push({ owner: filterUserId });
-      if (filterName != null) filter.$and.push({ name: { $regex: filterName, $options: 'i' } });
+      if (filterUserId != '') filter.$and.push({ owner: filterUserId });
+      if (filterName != '') filter.$and.push({ name: { $regex: filterName, $options: 'i' } });
       if (!getDuplicates) filter.$and.push({ $or: [{ isCopy: null }, { isCopy: false }] });
 
       let browseIncrement = parseInt(process.env.BROWSE_INCREMENT as string);