How can I force compiler to use default constructor when adding element to vector using emplace_back?

How can I force compiler to use default constructor when adding element to vector using emplace_back?

enum E {E1, E2};

struct A
{
  A(){}
  A(int i){}
};

void main()
{
  std::vector<std::pair<E, A>> testMap;

  testMap.emplace_back(E1, 10);
  // testMap.emplace_back(E2);
}

Commented out line gives following error: error C2664: 'std::pair<_Ty1,_Ty2>::pair(const std::pair<_Ty1,_Ty2> &)' : cannot convert parameter 1 from 'E' to 'const std::pair<_Ty1,_Ty2> &'