:checkered_flag: trying to fix C2440 error
:checkered_flag: trying to fix C2440 error

Error in AppVeyor:

unit-conversions.cpp(441): error C2440: 'initializing': cannot convert from 'nlohmann::json' to 'std::nullptr_t'

(https://ci.appveyor.com/project/nlohmann/json/build/2838/job/wo7im01sq6tvhe9m)

nlohmann/json,theodelrieu/json,nlohmann/json,theodelrieu/json,nlohmann/json