The new forum appears to have eaten my previous topic on this, so here goes again.
When I build Juce 4.2 in XCode with a target platform that is below 10.9, I get a build error because of std::nullptr_t (undefined).
In the meantime I found a solution, just exchange std::nullptr_t with decltype(nullptr). It would be nice if this could be patched, it’s just two lines.