diff --git a/lib/services/schema-object-factory.ts b/lib/services/schema-object-factory.ts
index 29b3165a9..9969aa08f 100644
--- a/lib/services/schema-object-factory.ts
+++ b/lib/services/schema-object-factory.ts
@@ -294,7 +294,7 @@ export class SchemaObjectFactory {
 
     if (!(enumName in schemas)) {
       schemas[enumName] = {
-        type: metadata.type as string,
+        type: metadata.type as string ?? 'string',
         enum:
           metadata.isArray && metadata.items
             ? metadata.items['enum']