Expected Behavior

When GitLab creates a branch that points to an existing commit, Pipelines as
Code should process the push webhook even when its commits array is empty.

For a valid branch-creation payload, the event should use the immutable after
SHA as the revision, resolve commit metadata for that exact SHA, and evaluate
PipelineRun definitions and repository-local task references from the same
source revision.

Actual Behavior

The GitLab provider rejects every push webhook whose commits array is empty:

no commits attached to this push event

GitLab can legitimately emit this shape when a new branch is created at an
existing commit. The event is discarded before repository matching, so no
PipelineRun is created for the new branch.

Steps to Reproduce the Problem

1. Configure a GitLab repository with Pipelines as Code.
2. Create a new branch that points to an existing commit without creating a new
   commit.
3. Deliver the resulting GitLab Push Hook. The relevant fields have this shape:

{
  "before": "0000000000000000000000000000000000000000",
  "after": "dc922f5ea0c57ef5fb1cbc0f3ea550dfe3b5786e",
  "ref": "refs/heads/release-0.1",
  "checkout_sha": "dc922f5ea0c57ef5fb1cbc0f3ea550dfe3b5786e",
  "commits": []
}

4. Observe that webhook parsing returns no commits attached to this push event, and no PipelineRun is triggered.

Additional Info

• Reproduced on the current main branch at
  9a97ed23075b15c7fa71f6622a13428c84c1d678.
• This is not Kubernetes-version specific; the event is rejected during webhook
  parsing.
• Branch deletion and unrelated empty-commit push events should continue to be
  rejected. A branch creation can be identified by a non-empty
  refs/heads/<branch> ref, an all-zero before SHA, and a valid non-zero
  40-character hexadecimal after SHA.
• The after SHA should be authoritative. Looking up the mutable branch name can
  race with a later push and resolve metadata or PipelineRun definitions from a
  different commit.

This report was prepared with assistance from OpenAI Codex (GPT-5) and was
reviewed and validated by the submitter.