findPrevious method
Checks if the specified key is already associated with a previous exchange and otherwise associates the key with the exchange specified.
Implementation
@override
CoapExchange? findPrevious(final int? key, final CoapExchange exchange) {
CoapExchange? prev;
if (_maps[_first].containsKey(key)) {
prev = _maps[_first][key];
}
_maps[_first][key] = exchange;
if (prev != null || _first == _second) {
return prev;
}
if (_maps[_second].containsKey(key)) {
prev = _maps[_second][key];
}
_maps[_second][key] = exchange;
return prev;
}