public static <K extends Comparable, V> TreeMap<K, V> newTreeMap() {
        return new TreeMap<>();
    }
Creates a <i>mutable</i>, empty {@code TreeMap} instance using the natural ordering of its
elements.

<p><b>Note:</b> if mutability is not required, use ImmutableSortedMap.of() instead.

<p><b>Note for Java 7 and later:</b> this method is now unnecessary and should be treated as
deprecated. Instead, use the {@code TreeMap} constructor directly, taking advantage of the new
<a href="http://goo.gl/iz2Wi">"diamond" syntax</a>.

@return a new, empty {@code TreeMap}
fastexcel-core/src/main/java/cn/idev/excel/util/MapUtils.java