diff --git a/lib/helpers/query/cast$expr.js b/lib/helpers/query/cast$expr.js
index 677e77f65f7..f7c7fe0521f 100644
--- a/lib/helpers/query/cast$expr.js
+++ b/lib/helpers/query/cast$expr.js
@@ -77,8 +77,8 @@ module.exports = function cast$expr(val, schema, strictQuery) {
 };
 
 function _castExpression(val, schema, strictQuery) {
-  if (isPath(val)) {
-    // Assume path
+  // Preserve the value if it represents a path or if it's null
+  if (isPath(val) || val === null) {
     return val;
   }