bt_factory.h uses nlohmann::json but does not include it

[Kikadass]

Describe the bug
bt_factory.h uses nlohmann::json but does not include it

I am getting error LNK2019 unresolved external symbol and fatal error LNK1120: 1 unresolved externals because I am trying to use bt_factory.h and I need to include nlohmann::json right before it, as bt_factory.h is not including it itself.

How to Reproduce*

Make a program where json is not used, include bt_factory.h and use parts of bt_factory.h. Such as the DecoratorNode, PortList, NodeConfig, NodeStatus and BehaviorTreeFactory.

Do not include nlohmann/json.hpp yourself. See the link error appear.
Only when including nlohmann/json.hpp right before the include bt_factory.h the linking error vanishes.