code: func ValidateEnvRequestedVersions() []unversioned.GroupVersion {
  	var missingVersions []unversioned.GroupVersion
  	for v := range envRequestedVersions {
  		if _, found := enabledVersions[v]; !found {
  			missingVersions = append(missingVersions, v)
  		}
  	}
  	return missingVersions
  }
docs: // ValidateEnvRequestedVersions returns a list of versions that are requested in
  // the KUBE_API_VERSIONS environment variable, but not enabled.