* the License.
 */

package com.google.common.base;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtCompatible;
import java.util.Collections;
import java.util.Set;
import javax.annotation.CheckForNull;

/** Implementation of an {@link Optional} not containing a reference. */
@GwtCompatible
@ElementTypesAreNonnullByDefault

 * the License.
 */

package com.google.common.base;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtCompatible;
import java.util.Collections;
import java.util.Set;
import javax.annotation.CheckForNull;

/** Implementation of an {@link Optional} containing a reference. */
@GwtCompatible
@ElementTypesAreNonnullByDefault

### 💯

* 1️⃣0️⃣0️⃣ 💯 <abbr title="The amount of code that is automatically tested">💯 💰</abbr>.
* 1️⃣0️⃣0️⃣ 💯 <abbr title="Python type annotations, with this your editor and external tools can give you better support">🆎 ✍</abbr> 📟 🧢.
* ⚙️ 🏭 🈸.

## 💃 ⚒

But Python has a specific way to declare lists with internal types, or "type parameters":

### Import typing's `List`

In Python 3.9 and above you can use the standard `list` to declare these type annotations as we'll see below. 💡

But in Python versions before 3.9 (3.6 and above), you first need to import `List` from standard Python's `typing` module:

```Python hl_lines="1"

 * limitations under the License.
 */

package com.google.common.collect;

import com.google.common.annotations.GwtCompatible;
import java.io.Serializable;
import java.util.List;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * An ordering that treats all references as equals, even nulls.
 *

 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtCompatible;
import java.io.Serializable;
import java.util.Comparator;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/** An ordering for a pre-existing comparator. */
@GwtCompatible(serializable = true)

 * limitations under the License.
 */

package com.google.common.collect;

import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Predicate;
import java.util.List;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Implementation of {@link Multimaps#filterKeys(ListMultimap, Predicate)}.
 *

 *
 * @author Chris Nokleberg
 */
@CheckReturnValue
@ParametersAreNonnullByDefault
package com.google.common.io;

import com.google.errorprone.annotations.CheckReturnValue;

 * limitations under the License.
 */

package com.google.common.collect;

import com.google.common.annotations.GwtCompatible;
import java.io.Serializable;
import java.util.List;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * An ordering that treats all references as equals, even nulls.
 *

 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect.testing.google;

import com.google.common.annotations.GwtCompatible;
import com.google.common.collect.Multiset;
import com.google.common.collect.testing.TestCollectionGenerator;
import org.checkerframework.checker.nullness.qual.Nullable;

/**