}
}

// in plugin
existingThing = objects.newInstance(DefaultExistingThing.class)
existingThing.convention("some-value")
```

It's not acceptable to treat an unset Provider as if the convention is requested when the convention could be set elsewhere:

```groovy
public interface NewThing {
    Property<String> getSomeProperty()
}

// Unacceptable
String value

  optional string scope = 4;

  // namespace is the namespace of the resource being referenced. This field is
  // required when scope is set to "Namespace" and must be unset when scope is set to
  // "Cluster".
  // +optional
  optional string namespace = 5;
}

// IngressClassSpec provides information about the class of an Ingress.
message IngressClassSpec {

* `path` - The file path to the file to stream.
* `headers` - Any custom headers to include, as a dictionary.
* `media_type` - A string giving the media type. If unset, the filename or path will be used to infer a media type.
* `filename` - If set, this will be included in the response `Content-Disposition`.

// the file it describes, it may be necessary to modify the Name field
// of the returned header to provide the full path name of the file.
// If compression is desired, callers should set the FileHeader.Method
// field; it is unset by default.
func FileInfoHeader(fi fs.FileInfo) (*FileHeader, error) {
	size := fi.Size()
	fh := &FileHeader{
		Name:               fi.Name(),
		UncompressedSize64: uint64(size),
	}
	fh.SetModTime(fi.ModTime())

  // +optional
  optional k8s.io.apimachinery.pkg.apis.meta.v1.Time lastUpdateTime = 4;

  // lastTransitionTime is the time the condition last transitioned from one status to another.
  // If unset, when a new condition type is added or an existing condition's status is changed,
  // the server defaults this to the current time.
  // +optional
  optional k8s.io.apimachinery.pkg.apis.meta.v1.Time lastTransitionTime = 5;
}

  // Some pod and container fields are restricted if this is set.
  //
  // If the OS field is set to linux, the following fields must be unset:
  // -securityContext.windowsOptions
  //
  // If the OS field is set to windows, following fields must be unset:
  // - spec.hostPID
  // - spec.hostIPC
  // - spec.hostUsers
  // - spec.securityContext.seLinuxOptions
  // - spec.securityContext.seccompProfile

	// MINIO_KMS_SECRET_KEY_FILE - either to the argument passed to
	// the container or to a default string (e.g. "minio_master_key").
	//
	// We have to distinguish a explicit config from an implicit. Hence,
	// we unset the env. vars if they are set but empty or contain a path
	// which does not exist. The downside of this check is that if
	// MINIO_KMS_SECRET_KEY_FILE is set to a path that does not exist,

  /** Singleton placeholder that indicates a value is being loaded. */
  @SuppressWarnings("unchecked") // impl never uses a parameter or returns any non-null value
  static <K, V> ValueReference<K, V> unset() {
    return (ValueReference<K, V>) UNSET;
  }

  private enum NullEntry implements ReferenceEntry<Object, Object> {
    INSTANCE;

    @CheckForNull
    @Override

  if [[ -z "${CONFIG}" ]]; then
    # Kubernetes 1.15+
    CONFIG=${DEFAULT_CLUSTER_YAML}
  fi

  KIND_WAIT_FLAG="--wait=180s"
  KIND_DISABLE_CNI="false"
  if [[ -n "${KUBERNETES_CNI:-}" ]]; then
    unset KIND_WAIT_FLAG
    KIND_DISABLE_CNI="true"
  fi

  # Create KinD cluster
  if ! (yq eval "${CONFIG}" --expression ".networking.disableDefaultCNI = ${KIND_DISABLE_CNI}" \

  // selector is the string-encoded form of a standard kubernetes label selector for the given metric
  // When set, it is passed as an additional parameter to the metrics server for more specific metrics scoping.
  // When unset, just the metricName will be used to gather metrics.
  // +optional
  optional k8s.io.apimachinery.pkg.apis.meta.v1.LabelSelector selector = 2;
}

// MetricSpec specifies how to scale based on a single metric