C++ call to list constructor is ambiguous

I'm trying to build an old C++ project on a modern version of Clang and getting lots of ambiguous errors. I don't have much C++ experience so apologies if this is basic stuff.

/home/ubuntu/NameAndTypeResolver.cpp:124:40: error: call to constructor of 'list<list<const dev::libcrunch::ContractDefinition *> >' is ambiguous
        list<list<ContractDefinition const*>> input(1, {});
                                              ^     ~~~~~

I'm not sure what the compilers asking for here. Additionally what is the {} syntax?