diff --git a/src/mongoose/buildQuery.js b/src/mongoose/buildQuery.js
index e23acd3f28..393baa4a27 100644
--- a/src/mongoose/buildQuery.js
+++ b/src/mongoose/buildQuery.js
@@ -177,7 +177,7 @@ class ParamParser {
     }
 
     if (schemaObject && schemaObject.ref && val === 'null') {
-      val = null;
+      formattedValue = null;
     }
 
     if (operator && validOperators.includes(operator)) {