Is it possible to use exceptions istead of assertions?

[lesf0]

Let's consider the following code

#include "json.hpp"
#include <iostream>

int main()
{
	const auto data = R"({"foo":42})"_json;
	
	try {
		std::cout << data["bar"] << std::endl;
	} catch(...) {
		std::cerr << "json error" << std::endl;
	}
}

I expect this code to output json error, but instead it shuts down with the following error:

json.hpp:12936: const value_type& nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer>::operator[](T*) const [with T = const char; ObjectType = std::map; ArrayType = std::vector; StringType = std::__cxx11::basic_string<char>; BooleanType = bool; NumberIntegerType = long int; NumberUnsignedType = long unsigned int; NumberFloatType = double; AllocatorType = std::allocator; JSONSerializer = nlohmann::adl_serializer; nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer>::const_reference = const nlohmann::basic_json<>&; nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer>::value_type = nlohmann::basic_json<>]: Assertion `m_value.object->find(key) != m_value.object->end()' failed.

I know I can disable assertion by NDEBUG flag, but then it prints out null in my example (and I'm almost sure this is an UB) instead of expected exception.

I've checked out json.hpp code and found 98 calls to assert, so I don't think above is the only example leading to application shutdown which can't be handled. In my real app I deal with user provided data, so it's quite bad for me. Is it possible to just replace those assertions with exception throws? Or, if assertions are necessary for some cases, is it possible to have something like template parameter specifying assertion handler, which would be defaulted to assert?

I can create a PR by myself, but first I want to know which option is preferred.

[nlohmann]

You can use the at function just like for std::map.

[lesf0]

I know I can, but unlike std::map this library allows const [] operator compilation, so I think it should be either disallowed or properly asserted to avoid possible problems.

[nlohmann]

This has been discussed several times. The operator[] will stay as is.

[nlohmann]

On assertions, please note the first entry in the README: https://github.com/nlohmann/json#notes.