*
     * @return an {@link Optional} containing the list of core extensions, or empty if not configured
     */
    @Nonnull
    Optional<List<CoreExtension>> coreExtensions();

    /**
     * Returns the options associated with this invocation request.
     *
     * @return the options object
     */
    @Nonnull
    O options();

        // v1 == 0.
        .optional(defaultValue = 0),
      Adapters.INTEGER_AS_BIG_INTEGER,
      algorithmIdentifier,
      name,
      validity,
      name,
      subjectPublicKeyInfo,
      Adapters.BIT_STRING.withTag(tag = 1L).optional(),
      Adapters.BIT_STRING.withTag(tag = 2L).optional(),
      extension.asSequenceOf().withExplicitBox(tag = 3).optional(defaultValue = listOf()),
      decompose = {

            throw new LookupException(e);
        }
    }

    @Override
    public <T> Optional<T> lookupOptional(Class<T> type) {
        try {
            return Optional.of(container.lookup(type));
        } catch (ComponentLookupException e) {
            if (e.getCause() instanceof NoSuchElementException) {
                return Optional.empty();
            }
            throw new LookupException(e);
        }
    }

  // +optional
  optional k8s.io.apimachinery.pkg.apis.meta.v1.ObjectMeta metadata = 1;

  // provisioner indicates the type of the provisioner.
  optional string provisioner = 2;

  // parameters holds the parameters for the provisioner that should
  // create volumes of this storage class.
  // +optional
  map<string, string> parameters = 3;

   *
   * <p><b>Java 9 users:</b> use {@code optional.stream()} instead.
   */
  @Beta
  @InlineMe(replacement = "optional.stream()")
  @InlineMeValidationDisabled("Java 9+ API only")
  public static <T> Stream<T> stream(java.util.Optional<T> optional) {
    return optional.isPresent() ? Stream.of(optional.get()) : Stream.empty();
  }

  /**
   * If a value is present in {@code optional}, returns a stream containing only that element,

  // name is allowed to be "" to represent the legacy, ungroupified resources.
  // More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#metadata
  // +optional
  optional k8s.io.apimachinery.pkg.apis.meta.v1.ObjectMeta metadata = 1;

  // versions are the versions supported in this group. They are sorted in descending order of preference,
  // with the preferred version being the first entry.

  optional string type = 1;

  // Status of the condition, one of True, False, Unknown.
  // +required
  optional string status = 2;

  // If set, this represents the .metadata.generation that the condition was set based upon.
  // +optional
  optional int64 observedGeneration = 3;

  // Last time the condition transitioned from one status to another.
  // +required

from typing import Optional

from fastapi import FastAPI
from fastapi.testclient import TestClient
from pydantic import BaseModel

app = FastAPI()


class SubModel(BaseModel):
    a: Optional[str] = "foo"


class Model(BaseModel):
    x: Optional[int] = None
    sub: SubModel


class ModelSubclass(Model):
    y: int
    z: int = 0
    w: Optional[int] = None


class ModelDefaults(BaseModel):

@REM
@REM   JAVA_HOME           (Optional) Points to a Java installation.
@REM   MAVEN_BATCH_ECHO    (Optional) Set to 'on' to enable the echoing of the batch commands.
@REM   MAVEN_BATCH_PAUSE   (Optional) set to 'on' to wait for a key stroke before ending.
@REM   MAVEN_OPTS          (Optional) Java runtime options used when Maven is executed.
@REM   MAVEN_SKIP_RC       (Optional) Flag to disable loading of mavenrc files.

  // +optional
  optional k8s.io.apimachinery.pkg.apis.meta.v1.DeleteOptions deleteOptions = 2;
}

// PodDisruptionBudget is an object to define the max disruption that can be caused to a collection of pods
message PodDisruptionBudget {
  // Standard object's metadata.
  // More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#metadata
  // +optional