extend method Null safety

Runtime extend(
  1. String name,
  2. String identifier

Returns a child of this that counts as both this platform's identifier and the new identifier.

This may not be called on a platform that's already a child.


Runtime extend(String name, String identifier) {
  if (parent == null) return Runtime._child(name, identifier, this);
  throw StateError('A child platform may not be extended.');