diff --git a/workflow-parser/src/workflows/yaml-object-reader.ts b/workflow-parser/src/workflows/yaml-object-reader.ts
index ce93d9ab..8c18680c 100644
--- a/workflow-parser/src/workflows/yaml-object-reader.ts
+++ b/workflow-parser/src/workflows/yaml-object-reader.ts
@@ -77,7 +77,7 @@ export class YamlObjectReader implements ObjectReader {
     if (isPair(node)) {
       const scalarKey = node.key as Scalar;
       range = this.getRange(scalarKey);
-      const key = scalarKey.value as string;
+      const key = scalarKey.value === null ? "" : String(scalarKey.value);
       yield new ParseEvent(EventType.Literal, new StringToken(this.fileId, range, key, undefined));
       for (const child of this.getNodes(node.value)) {
         yield child;