default config doesn't work when there's a wait: true

[jamietanna]

When using the new default configuration released as part of #20 / #29, it appears that this does not work in conjunction with the wait: true

For the following Buildkite configuration:

steps:
  - label: "Triggering pipelines"
    plugins:
      monorepo-diff#v1.1.0:
        diff: ".buildkite/diff ${BUILDKITE_COMMIT}"
        wait: true
        watch:
          - path: "renovate.json"
            config:
              label: "Verify Renovate configuration"
              command: "renovate-config-validator"
              agents:
                # ...

          # ... otherwise, fall back to the default pipeline
          - default:
              config:
                label: ":pipeline: Upload default Pipeline"
                command: "buildkite-agent pipeline upload .buildkite/default-pipeline.yml"

This then fails to run:

$ /buildkite-agent/plugins/.../github-com-buildkite-plugins-monorepo-diff-buildkite-plugin-v1-1-0/hooks/command
INFO[0000] --- running monorepo-diff-buildkite-plugin 1.1.0
INFO[2024-10-23T08:45:46Z] Running diff command: .buildkite/diff d5e161b1e7c95f41861f0c84b73d5097175a5328
Generated Pipeline:
steps:
- {}
- wait: null
FATA[2024-10-23T08:45:48Z] +++ failed to upload pipeline: command `buildkite-agent` failed: exit status 1
🚨 Error: The command exited with status 1
user command error: The plugin monorepo-diff command hook exited with status 1