in dfp/include/DecimalNative.hpp [1128:1135]
static Decimal64_t subtractChecked(Decimal64_t const& a, Decimal64_t const& b) {
if (a.isNull())
throw std::invalid_argument(DN_FUNC + ": Argument '" + DN_NAMEOF(a) + "' is null.");
if (b.isNull())
throw std::invalid_argument(DN_FUNC + ": Argument '" + DN_NAMEOF(b) + "' is null.");
return subtractUnchecked(a, b);
}