diff --git a/packages/core/src/lib/create-mapper/create-map-for-member.util.ts b/packages/core/src/lib/create-mapper/create-map-for-member.util.ts
index a61202a08..67f254315 100644
--- a/packages/core/src/lib/create-mapper/create-map-for-member.util.ts
+++ b/packages/core/src/lib/create-mapper/create-map-for-member.util.ts
@@ -59,7 +59,7 @@ export function createMapForMember<
       mapMemberFn[MapFnClassId.type] === TransformationType.MapWith) &&
     mapMemberFn[MapFnClassId.misc] != null
   ) {
-    sourcePath = getMemberPath(mapMemberFn[MapFnClassId.misc]);
+    sourcePath = getMemberPath(mapMemberFn[MapFnClassId.misc]!);
   }
 
   // initialize MappingProperty