public static <T> ToDoubleNullable<T> absDoubleOrNull(ToDoubleNullable<T> expression) {
        return new ToDoubleNullableImpl<>(
            absDouble(expression.orThrow()),
            expression.isNull()
        );
    }
Returns an expression that takes an expression and returns its absolute
(removing the negation sign if any). If the result of the original
expression is {@code null}, then the new expression will also return
{@code null}.

@param expression  the input expression
@param <T>         the input type
@return            the new expression
runtime-parent/runtime-compute/src/main/java/com/speedment/runtime/compute/internal/expression/AbsUtil.java