Description

NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT should not throw an exception when the json instance is empty and should use the default values of the member fields

Reproduction steps

run the Minimal code example and get the exception

Expected vs. actual results

don't expect to get exception with an empty JSON
expect that foo member fields are filled with they default values

Minimal code example

class Foo {
 public:
  NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(Foo, a, b)

  Foo() = default;

  int a{10};
  std::string b{"bar"};

  void log() {
    std::cout << "a: " << a << std::endl;
    std::cout << "b: " << b << std::endl;
  }
};

// with an empty json, an exception is thrown instead of getting default values
static void JsonTest_empty_json() {
  nlohmann::json json{};
  auto foo = Foo(json);
  foo.log();
}

int main(int argc, char **argv) {
  JsonTest_empty_json();
  return 0;
}

Error messages

No response

Compiler and operating system

clang++ / C++17 / Windows OS

Library version

ref: v3.11.2 - commit: 7d2f9ad500cf062394040f44d006791ff7cfc1c1

Validation

• The bug also occurs if the latest version from the develop branch is used.
• I can successfully compile and run the unit tests.