Summary
-------

Adding an isEmpty default method to CharSequence would harmonize String with other CharSequence implementations (StringBuilder etc). 

Problem
-------

isEmpty is shorter and more concise than length() == 0. Checking for and filtering out empty Strings and other CharSequences is a common occurrence in code, and having an explicit method allows its use as a method reference. 

Solution
--------

Add a default method isEmpty() to CharSequence.

Specification
-------------

Add the following to java.lang.CharSequence:

    /**
     * Returns {@code true} if this character sequence is empty.
     *
     * @implSpec
     * The default implementation returns the result of calling {@code length() == 0}.
     *
     * @return {@code true} if {@link #length()} is {@code 0}, otherwise
     * {@code false}
     *
     * @since 15
     */
    default boolean isEmpty() {
        return this.length() == 0;
    }

Also add an override with clarifications to java.nio.CharBuffer:

    /**
     * Returns {@code true} if this character buffer is empty.
     *
     * @return {@code true} if there are {@code 0} remaining characters,
     *         otherwise {@code false}
     *
     * @since 15
     */
    public final boolean isEmpty() {
        return remaining() == 0;
    }