get_transitions() ======//maybe it is a crash

[405092901]

transition_collection get_transitions() const {
transition_collection result;
for (auto it = d_success.cbegin(); it != d_success.cend(); ++it) {
result.push_back(it->first); //maybe it is a crash
}
return transition_collection(result);
}

code:result.push_back(it->first);

i found it sometimes crash