**
 * An implementation of {@code RangeMap} based on a {@code TreeMap}, supporting
 * all optional operations.
 *
 * <p>Like all {@code RangeMap} implementations, this supports neither null
 * keys nor null values.
**
 * An implementation of {@code RangeMap} based on a {@code TreeMap}, supporting
 * all optional operations.
 *
 * <p>Like all {@code RangeMap} implementations, this supports neither null
 * keys nor null values. | TreeRangeMap.java