static <T, R> MapperFunction<T, R> of(Function<? super T, ? extends R> function) {
            requireNonNull(function, "function");
            return o -> {
                final R result = function.apply(o);
                requireNonNull(result, "function.apply() returned null");
                return result;
            };
        }
Creates a new {@link MapperFunction} from the specified {@link Function}.
core/src/main/java/com/linecorp/armeria/common/stream/FuseableStreamMessage.java