fmt::is_formattable<void>::value == false

In file included from /opt/compiler-explorer/libs/fmt/trunk/include/fmt/format.h:41,
                 from <source>:1:
/opt/compiler-explorer/libs/fmt/trunk/include/fmt/base.h: In substitution of 'template<class T, class Char> using is_formattable = fmt::v11::bool_constant<(! std::is_base_of<fmt::v11::detail::unformattable, decltype (fmt::v11::detail::arg_mapper<Char>::map(declval<T&>()))>::value)> [with T = void; Char = char]':
<source>:6:44:   required from here
/opt/compiler-explorer/libs/fmt/trunk/include/fmt/base.h:1269:73: error: forming reference to void
 1269 | using mapped_t = decltype(detail::arg_mapper<Char>::map(std::declval<T&>()));
      |                                                         ~~~~~~~~~~~~~~~~^~
Execution build compiler returned: 1