createRelative method
The resource at relativePath from this one, such as a sibling file
next to a config file. It is not checked to exist. Throws
UnsupportedError for resources without a location (bytes in
memory).
final dev = resource.createRelative('application-dev.properties');
Implementation
@override
Resource createRelative(String relativePath) => throw UnsupportedError(
'Cannot create a relative resource for $description',
);