check method
Implementation
DSX<T> check() {
var objSrc = _dsxToObjectSource[this];
var obj = _dsxToObject[this];
if (objSrc == null && obj == null) {
_dsxToObjectSource[this] = null;
_dsxToObject[this] = null;
_keyToDSK.remove(_key);
}
return this;
}