public static <C, U, V> Mapper<C, U, V, Pair<U, V>> defaultMapper() {
        return (ctx, u, v) -> ArgumentParseResult.successFuture(Pair.of(u, v));
    }
Creates the default mapper that simply returns a {@link Pair} of the two input values.

@param <C> the command sender type
@param <U> the first type
@param <V> the second type
@return a default mapper that returns a {@link Pair} of the two input values
cloud-core/src/main/java/org/incendo/cloud/parser/aggregate/AggregateParserPairBuilder.java