diff --git a/packages/form-js-viewer/src/util/index.js b/packages/form-js-viewer/src/util/index.js
index d61cc313a..193e6a057 100644
--- a/packages/form-js-viewer/src/util/index.js
+++ b/packages/form-js-viewer/src/util/index.js
@@ -152,7 +152,7 @@ export function getSchemaVariables(schema, options = {}) {
 
     }
 
-    return variables.filter(variable => variable !== undefined || variable !== null);
+    return variables.filter(variable => typeof variable === 'string');
   }, []);
 
   const getBindingVariables = (node)=> {