fix(challenges): handle case where challenge has no categories or result is empty

website/server/libs/challenges/index.js

@@ -117,6 +117,9 @@ export function createChallengeQuery (query) {
     .match(query)
     .addFields({
       isOfficial: {
+        $cond: {
+          if: { $isArray: '$categories' },
+          then: {
             $gt: [
               {
                 $size: {
@@ -132,6 +135,9 @@ export function createChallengeQuery (query) {
               0,
             ],
           },
+          else: false,
+        },
+      },
     })
     .sort('-isOfficial -createdAt');
 }