* @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
   *     {@code null}) and returns {@code Optional.empty()} if it has none.
   */
  @SuppressWarnings("unchecked")
  public static <T> Collector<T, ?, Optional<T>> toOptional() {
    return (Collector) TO_OPTIONAL;

import java.util.Collections;
import java.util.Iterator;
import org.junit.Ignore;

/**
 * Tests for {@link Multimap#putAll(Object, Iterable)}.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
@Ignore("test runners must not instantiate and run this directly, only via suites we build")
@SuppressWarnings({
  // @Ignore affects the Android test runner, which respects JUnit 4 annotations on JUnit 3 tests.
  "JUnit4ClassUsedInJUnit3",

This is particularly so if the compression ratio of your content reveals information about it.
See [CRIME TLS](https://en.wikipedia.org/wiki/CRIME) as an example of this.

Therefore, compression is disabled when encrypting by default, and must be enabled separately.

Consult our security experts on [SUBNET](https://min.io/pricing) to help you evaluate if
your setup can use this feature combination safely.

To enable compression+encryption use:

```bash

import org.jspecify.annotations.Nullable;
import org.junit.Ignore;

/**
 * Tester for {@code Multimap.equals}.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
@Ignore("test runners must not instantiate and run this directly, only via suites we build")
// @Ignore affects the Android test runner, which respects JUnit 4 annotations on JUnit 3 tests.
@SuppressWarnings("JUnit4ClassUsedInJUnit3")
@NullMarked

import java.util.Collection;
import org.junit.Ignore;

/**
 * Tests for {@link Multimap#removeAll(Object)}.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
@Ignore("test runners must not instantiate and run this directly, only via suites we build")
// @Ignore affects the Android test runner, which respects JUnit 4 annotations on JUnit 3 tests.
@SuppressWarnings("JUnit4ClassUsedInJUnit3")

 * please see {@link com.google.common.collect.testing.MapTestSuiteBuilder}.
 *
 * @author George van den Driessche
 * @author Chris Povirk
 */
@GwtCompatible
@Ignore("test runners must not instantiate and run this directly, only via suites we build")
// @Ignore affects the Android test runner, which respects JUnit 4 annotations on JUnit 3 tests.
@SuppressWarnings("JUnit4ClassUsedInJUnit3")

 * required but is fulfilled by all current implementations.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
@Ignore("test runners must not instantiate and run this directly, only via suites we build")
// @Ignore affects the Android test runner, which respects JUnit 4 annotations on JUnit 3 tests.
@SuppressWarnings("JUnit4ClassUsedInJUnit3")

 * {@link com.google.common.collect.testing.MapTestSuiteBuilder}.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
@Ignore("test runners must not instantiate and run this directly, only via suites we build")
// @Ignore affects the Android test runner, which respects JUnit 4 annotations on JUnit 3 tests.
@SuppressWarnings("JUnit4ClassUsedInJUnit3")

 * directly; please see {@link com.google.common.collect.testing.MapTestSuiteBuilder}.
 *
 * @author Kevin Bourrillion
 * @author Louis Wasserman
 */
@GwtCompatible
@Ignore("test runners must not instantiate and run this directly, only via suites we build")
// @Ignore affects the Android test runner, which respects JUnit 4 annotations on JUnit 3 tests.
@SuppressWarnings("JUnit4ClassUsedInJUnit3")

import java.util.Iterator;
import java.util.Map.Entry;
import org.junit.Ignore;

/**
 * Tester for {@code Multimap.entries}.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
@Ignore("test runners must not instantiate and run this directly, only via suites we build")
// @Ignore affects the Android test runner, which respects JUnit 4 annotations on JUnit 3 tests.
@SuppressWarnings("JUnit4ClassUsedInJUnit3")