fix: inverted condition in dereferencable

include/serializer/strconv.h

@@ -24,7 +24,7 @@ inline std::string to_string(std::string_view str) { return std::string(str); }
 template <typename T> std::string to_string(T const & elem) {
   if constexpr (detail::is_dereferencable_v<T>) {
     using ::serializer::to_string;
-    return elem ? "nil" : to_string(*elem);
+    return elem ? to_string(*elem) : "nil";
   } else if constexpr (std::is_enum_v<T>) {
     constexpr auto type =
         magic_enum::as_flags<magic_enum::detail::is_flags_v<T>>;