script property Null safety
The absolute URI of the script being run in this isolate.
If the script argument on the command line is relative, it is resolved to an absolute URI before fetching the script, and this absolute URI is returned.
URI resolution only does string manipulation on the script path, and this may be different from the file system's path resolution behavior. For example, a symbolic link immediately followed by '..' will not be looked up.
@override Uri get script => _throwIfNull(_script);