s method
获取 value 转 string
Implementation
String s(String key, [String defaultValue = '']) {
final value = this[key];
if (value is String) return value;
if (value == null) {
XLog.d('$key=null => String:$defaultValue');
return defaultValue;
}
XLog.d('${value.runtimeType} $key=$value => String:$value');
return value.toString();
}