---
fixes:
  - |
    Zuul now treats job dependencies that reference undefined jobs as
    a configuration error.  Previously a job which depended on another
    job which did not exist would pass initial syntax validation and
    only cause a failure in freezing the job graph when Zuul attempted
    to run the job.  Now incorrect or missing job dependencies are
    detected during configuration.  This means that new config errors
    may be prevented from merging.  It also means that existing
    erroneous job or project configurations will be regarded as
    configuration errors at startup.