message: Fixed compilation error.
diff: @@ -67,7 +67,7 @@ void SigmaPrimitives<Exponent, GroupElement>::generate_challenge(
  const std::vector<GroupElement>& group_elements,
  Exponent& result_out) {
  if (group_elements.empty())
  - throw ZerocoinException("Group elements empty while generating a challenge.");
  + throw std::runtime_error("Group elements empty while generating a challenge.");
  CSHA256 hash;
  std::vector<unsigned char> data(group_elements.size() * group_elements[0].memoryRequired());
  unsigned char* current = data.data();
  