Hello everyone,
I’m facing a persistent issue in Vertex AI Agent Builder (Playbooks / Dialogflow CX) while trying to create/save a Production Environment. I keep getting the following error blocking the save action:
“Tool ‘null’ is referenced in version ‘Apr 24, 2026 01:39 PM’ of playbook ‘Mago do Billing’, but not included in the environment.”
Context & Troubleshooting done so far: This seems to be a ghost reference/cache issue related to a tool that was deleted or modified. I’ve tried everything to clear the references, but the UI keeps failing. Here is what I’ve done:
-
Cleaned Instructions: I removed all hardcoded
${TOOL:tool_name}references from the Playbook’s instructions. -
Re-linked Tools: I unchecked the tools, saved, re-checked them, and inserted them back into the instructions using the
@dropdown to ensure the internal ID is correct. -
Published Default Start Flow: I created a formal version for the “Default Start Flow” (it is NOT set to ‘Not published’ in the environment dropdown).
-
Synced Versions: I created fresh releases for the Playbook, the Tool (OpenAPI extension), and the Flow at the exact same time, and selected these brand-new versions in the Environment creation screen.
-
Hard Reset: I even tried recreating the agent from scratch, but the error persists when setting up the environment.
It looks like the environment validation is checking a stale dependency graph and failing to find an old tool ID, returning null.
Has anyone faced this “Tool ‘null’” ghost error? Is there any workaround to force the environment to save or a CLI command to bypass this UI validation bug?
Thanks in advance!
