in cxx/fbjni/detail/SimpleFixedString.h [208:220]
constexpr SimpleFixedString(
const Left& left,
std::size_t left_size,
const Right& right,
std::size_t right_size,
std::index_sequence<Is...>) noexcept
: data_{detail::fixedstring::char_at_(
left,
left_size,
right,
right_size,
Is)...,
'\0'},