diff --git a/lib/config.js b/lib/config.js
index 06a1b1a..b088583 100644
--- a/lib/config.js
+++ b/lib/config.js
@@ -307,7 +307,7 @@ async function getConfig() {
   if (attributesInput) {
     try {
       customAttributes = yaml.parse(attributesInput);
-      if (typeof customAttributes !== 'object' || Array.isArray(customAttributes)) {
+      if (customAttributes === null || typeof customAttributes !== 'object' || Array.isArray(customAttributes)) {
         throw new Error('Attributes must be a YAML object (key: value pairs)');
       }
       core.info(`Parsed ${Object.keys(customAttributes).length} custom attribute(s)`);