/guava/guava-gwt/src-super/com/google/common/collect/super/com/google/common/collect/ImmutableSortedMap.java
checkNotNull( fromKey) ;checkNotNull( valueFunction) ;
checkNotNull ( valueFunction ) ;
Comparator<? super K> comparator, Function<? super T, ? extends K> keyFunction, Function<? super T, ? extends V> valueFunction, BinaryOperator<V> mergeFunction) { checkNotNull(comparator); checkNotNull(keyFunction); <extra_id_0> checkNotNull(mergeFunction); return Collectors.collectingAndThen( Collectors.toMap( keyFunction, valueFunction, mergeFunction, () -> new TreeMap<K, V>(comparator)), ImmutableSortedMap::copyOfSorted); }