/**
   * A collector that converts a stream of zero or one elements to an {@code Optional}.
   *
   * @throws IllegalArgumentException if the stream consists of two or more elements.
   * @throws NullPointerException if any element in the stream is {@code null}.
   * @return {@code Optional.of(onlyElement)} if the stream has exactly one element (must not be

}

// ErrFilterNamePrefix - more than one prefix usage error.
type ErrFilterNamePrefix struct{}

func (err ErrFilterNamePrefix) Error() string {
	return "more than one prefix in filter rule"
}

// ErrFilterNameSuffix - more than one suffix usage error.
type ErrFilterNameSuffix struct{}

func (err ErrFilterNameSuffix) Error() string {
	return "more than one suffix in filter rule"
}

                        newHashSet("a", elements[0], "b"), newHashSet("c", elements[0], "d"));
                  }
                })
            .named("intersection with overlap of one")
            .withFeatures(CollectionSize.ONE, CollectionFeature.ALLOWS_NULL_VALUES)
            .createTestSuite());

    suite.addTest(
        SetTestSuiteBuilder.using(
                new TestStringSetGenerator() {

                        newHashSet("a", elements[0], "b"), newHashSet("c", elements[0], "d"));
                  }
                })
            .named("intersection with overlap of one")
            .withFeatures(CollectionSize.ONE, CollectionFeature.ALLOWS_NULL_VALUES)
            .createTestSuite());

    suite.addTest(
        SetTestSuiteBuilder.using(
                new TestStringSetGenerator() {

     * @param source A hint about the source of the problem like a file path, may be {@code null}.
     * @param lineNumber The one-based index of the line containing the problem or {@code -1} if unknown.
     * @param columnNumber The one-based index of the column containing the problem or {@code -1} if unknown.
     * @param exception The exception that caused this problem, may be {@code null}.
     */

        new Builder<String, Integer>().put(immutableEntry("one", 1)).build();
    assertEquals(asList(1), multimap.get("one"));
  }

  public void testBuilder_withImmutableEntryAndNullContents() {
    Builder<String, Integer> builder = new Builder<>();
    assertThrows(
        NullPointerException.class, () -> builder.put(immutableEntry("one", (Integer) null)));

<img src="/img/tutorial/separate-openapi-schemas/image03.png">
</div>

### Model for Input and Output in Docs

And if you check all the available Schemas (JSON Schemas) in OpenAPI, you will see that there are two, one `Item-Input` and one `Item-Output`.

For `Item-Input`, `description` is **not required**, it doesn't have a red asterisk.

But for `Item-Output`, `description` is **required**, it has a red asterisk.

<div class="screenshot">

     * @param severity The severity of the problem, must not be {@code null}.
     * @param message The detail message of the problem, may be {@code null}.
     * @param line The one-based index of the line containing the problem or {@code -1} if unknown.
     * @param column The one-based index of the column containing the problem or {@code -1} if unknown.
     * @param cause The cause of the problem, may be {@code null}.
     */

            // to). Our contract promises:
            //
            // 1. not to execute a new callable until the old one has returned
            //
            // If we were to cancel taskFuture, that would let the next task start while the old
            // one is still running.
            //
            // Now, maybe we could tweak our implementation to not start the next task until the

                  @Override
                  SetMultimap<String, Integer> filter(SetMultimap<String, Integer> multimap) {
                    multimap.put("one", 314);
                    multimap.put("two", 159);
                    multimap.put("one", 265);
                    return filterValues(
                        multimap, not(Predicates.in(ImmutableSet.of(314, 159, 265))));
                  }
                })