* exercise null handling fail on those subcollections.
   */
  public abstract static class NullsBefore implements Comparator<@Nullable String>, Serializable {
    /*
     * We don't serialize this class in GWT, so we don't care about whether GWT will serialize this
     * field.
     */
    @GwtTransient private final String justAfterNull;

    protected NullsBefore(String justAfterNull) {
      if (justAfterNull == null) {

		} else {
			versions = append(versions, fi)
			allVersionIDs = append(allVersionIDs, fi.VersionID)
		}
	}
	buf, err := xl.AppendTo(nil)
	if err != nil {
		t.Fatalf("Failed to serialize xlmeta %v", err)
	}
	fivs, err := getFileInfoVersions(buf, basefi.Volume, basefi.Name, false)
	if err != nil {
		t.Fatalf("getFileInfoVersions failed: %v", err)
	}
	chkNumVersions := func(fis []FileInfo) bool {

   * exercise null handling fail on those subcollections.
   */
  public abstract static class NullsBefore implements Comparator<@Nullable String>, Serializable {
    /*
     * We don't serialize this class in GWT, so we don't care about whether GWT will serialize this
     * field.
     */
    @GwtTransient private final String justAfterNull;

    protected NullsBefore(String justAfterNull) {
      if (justAfterNull == null) {

 * serialize collections that are defined elsewhere.
 *
 * @author Jared Levy
 */
@GwtIncompatible
@J2ktIncompatible
@ElementTypesAreNonnullByDefault
final class Serialization {
  private Serialization() {}

  /**
   * Reads a count corresponding to a serialized map, multiset, or multimap. It returns the size of

    Set<Object> uniqueEntries = Sets.newIdentityHashSet();
    uniqueEntries.addAll(bimap.entrySet());
    assertEquals(3, uniqueEntries.size());
  }

  @J2ktIncompatible
  @GwtIncompatible // serialize
  public void testSerializable() {
    SerializableTester.reserializeAndAssert(EnumHashBiMap.create(Currency.class));
  }

  @J2ktIncompatible
  @GwtIncompatible // reflection
  public void testNulls() {

     * @throws Exception
     */
    @Test
    public void testSerialize() throws Exception {
        list.addLast("1");
        list.addLast("2");
        list.addLast("3");
        assertThat(SerializeUtil.serialize(list), is(notNullValue()));
    }

    /**
     * @throws Exception
     */
    @Test
    public void testSet() throws Exception {
        list.addLast("1");
        list.addLast("2");

    assertEquals(Integer.valueOf(5), reserialize(Suppliers.ofInstance(5)).get());
    assertEquals(
        Integer.valueOf(5),
        reserialize(Suppliers.compose(Functions.identity(), Suppliers.ofInstance(5))).get());
    assertEquals(Integer.valueOf(5), reserialize(Suppliers.memoize(Suppliers.ofInstance(5))).get());
    assertEquals(
        Integer.valueOf(5),

    assertEquals(Integer.valueOf(5), reserialize(Suppliers.ofInstance(5)).get());
    assertEquals(
        Integer.valueOf(5),
        reserialize(Suppliers.compose(Functions.identity(), Suppliers.ofInstance(5))).get());
    assertEquals(Integer.valueOf(5), reserialize(Suppliers.memoize(Suppliers.ofInstance(5))).get());
    assertEquals(
        Integer.valueOf(5),

	log.SetPrefix("go_android_exec: ")
	exitCode, err := runMain()
	if err != nil {
		log.Fatal(err)
	}
	os.Exit(exitCode)
}

func runMain() (int, error) {
	// Concurrent use of adb is flaky, so serialize adb commands.
	// See https://github.com/golang/go/issues/23795 or
	// https://issuetracker.google.com/issues/73230216.
	lockPath := filepath.Join(os.TempDir(), "go_android_exec-adb-lock")

```

</div>

Then go to the `/docs` UI, you will see that **FastAPI** is using these **models** to **document** the API, and it will use them to **serialize** and **validate** the data too.

<div class="screenshot">
<img src="/img/tutorial/sql-databases/image01.png">
</div>

## Update the App with Multiple Models