SetMap method
don't use this method to set null, because map entries with value of null will be ignored
Implementation
UpdateStatement SetMap(Map<String, dynamic> map) {
this._assigns = map.entries
.where((item) => item.value != null)
.map<Assignment>((item) => new Assignment(item.key, new ValueExpr.Name(item.key, item.value)))
.toList();
return this;
}