* default rounding mode: if the two nearest representable values are equally near, the one with
   * the least significant bit zero is chosen. (In such cases, both of the nearest representable
   * values are even integers; this method returns the one that is a multiple of a greater power of
   * two.)
   *
   * @throws ArithmeticException if {@code mode} is {@link RoundingMode#UNNECESSARY} and {@code x}

   * the {@code x} and {@code y} values must both have non-zero population variance (i.e. {@code
   * xStats().populationVariance() > 0.0 && yStats().populationVariance() > 0.0}). The result is not
   * guaranteed to be exactly +/-1 even when the data are perfectly (anti-)correlated, due to
   * numerical errors. However, it is guaranteed to be in the inclusive range [-1, +1].
   *
   * <h3>Non-finite values</h3>
   *

   * rather than just the {@link RuntimeException} or {@link Error} that should be possible. (And in
   * fact the static type of {@link Throwable} is occasionally justified even for a method with no
   * {@code throws} clause: Some such methods can in fact throw a checked exception (e.g., by
   * calling code written in Kotlin).) Typically, we want to let a {@link Throwable} from such a

   * rather than just the {@link RuntimeException} or {@link Error} that should be possible. (And in
   * fact the static type of {@link Throwable} is occasionally justified even for a method with no
   * {@code throws} clause: Some such methods can in fact throw a checked exception (e.g., by
   * calling code written in Kotlin).) Typically, we want to let a {@link Throwable} from such a

 *       of the type argument supplied by the user of the class: For example, {@code
 *       ImmutableMap.get} returns {@code @Nullable E} because the method can return {@code null}
 *       even on an {@code ImmutableMap<K, @NonNull String>}.
 * </ul>
 *
 * <p>Consumers of this annotation include:
 *
 * <ul>
 *   <li>NullAway, which <a

 *       of the type argument supplied by the user of the class: For example, {@code
 *       ImmutableMap.get} returns {@code @Nullable E} because the method can return {@code null}
 *       even on an {@code ImmutableMap<K, @NonNull String>}.
 * </ul>
 *
 * <p>Consumers of this annotation include:
 *
 * <ul>
 *   <li>NullAway, which <a

 *       of the type argument supplied by the user of the class: For example, {@code
 *       ImmutableMap.get} returns {@code @Nullable E} because the method can return {@code null}
 *       even on an {@code ImmutableMap<K, @NonNull String>}.
 * </ul>
 *
 * <p>Consumers of this annotation include:
 *
 * <ul>
 *   <li>NullAway, which <a

 *       of the type argument supplied by the user of the class: For example, {@code
 *       ImmutableMap.get} returns {@code @Nullable E} because the method can return {@code null}
 *       even on an {@code ImmutableMap<K, @NonNull String>}.
 * </ul>
 *
 * <p>Consumers of this annotation include:
 *
 * <ul>
 *   <li>NullAway, which <a

 *       of the type argument supplied by the user of the class: For example, {@code
 *       ImmutableMap.get} returns {@code @Nullable E} because the method can return {@code null}
 *       even on an {@code ImmutableMap<K, @NonNull String>}.
 * </ul>
 *
 * <p>Consumers of this annotation include:
 *
 * <ul>
 *   <li>NullAway, which <a

 *       of the type argument supplied by the user of the class: For example, {@code
 *       ImmutableMap.get} returns {@code @Nullable E} because the method can return {@code null}
 *       even on an {@code ImmutableMap<K, @NonNull String>}.
 * </ul>
 *
 * <p>Consumers of this annotation include:
 *
 * <ul>
 *   <li>NullAway, which <a