code: public static <T> BinaryOperator<T> mutate(BiConsumer<T, T> mutator) {
      Ensure.that(mutator != null, "mutator != null");
  
      return (left, right) -> consumeAndReturn(mutator, left, right);
    }
docs: <p>The intent is to use the given consumer to mutate the left argument and then return it.</p>
  <p>
  Example: {@code BinaryOperator<List<String>> combiner = Combiners.mutate(List::addAll); }
  </p>
  <p>
  The result is equivalent to {@code BinaryOperator<List<String>> combiner = (left, right) -> { left.addAll(right); return left; } }
  </p>
  
  @param mutator mutates the left argument to add data from the right argument
  @param <T> the container type
  @return a binary operator
  @see java.util.stream.Collector#combiner()