(opt) add Optional.isEmpty

Summary

A new method isEmpty which would return true if the corresponding Optional does not have a value. Else, it would return false. The proposed method is to be added in Optional, OptionalInt, OptionalDouble and OptionalLong classes.

Problem

A method isPresent is available now in Optional, OptionalInt, OptionalDouble and OptionalLong classes. It would be helpful to have its inverse Optional.isEmpty as well.

Solution

A new method isEmpty in Optional, OptionalInt, OptionalLong and OptionalDouble classes.

Specification

/src/java.base/share/classes/java/util/Optional.java

     /**
+     * If a value is not present, returns {@code true}, otherwise
+     * {@code false}.
+     *
+     * @return  {@code true} if a value is not present, otherwise {@code false}
+     * @since   11
+     */
+    public boolean isEmpty() {

/src/java.base/share/classes/java/util/OptionalDouble.java

     /**
+     * If a value is not present, returns {@code true}, otherwise
+     * {@code false}.
+     *
+     * @return  {@code true} if a value is not present, otherwise {@code false}
+     * @since   11
+     */
+    public boolean isEmpty() {

/src/java.base/share/classes/java/util/OptionalInt.java

     /**
+     * If a value is not present, returns {@code true}, otherwise
+     * {@code false}.
+     *
+     * @return  {@code true} if a value is not present, otherwise {@code false}
+     * @since   11
+     */
+    public boolean isEmpty() {

/src/java.base/share/classes/java/util/OptionalLong.java

     /**
+     * If a value is not present, returns {@code true}, otherwise
+     * {@code false}.
+     *
+     * @return  {@code true} if a value is not present, otherwise {@code false}
+     * @since   11
+     */
+    public boolean isEmpty() {