feat(search-backend-node): check types in error handling

Co-authored-by: Emma Indal <emma.indahl@gmail.com>
Signed-off-by: Camila Belo <camilaibs@gmail.com>

plugins/search-backend-node/src/engines/LunrSearchEngine.ts

@@ -168,7 +168,7 @@ export class LunrSearchEngine implements SearchEngine {
       type => !documentTypes || documentTypes.includes(type),
     );
 
-    if (!indexKeys.length) {
+    if (documentTypes?.length && !indexKeys.length) {
       throw new MissingIndexError(
         `Missing index for ${documentTypes?.toString()}. This means there are no documents to search through.`,
       );