copy method Null safety
- String newPath
Copies this file.
newPath is a relative path, it is resolved against
the current working directory (Directory.current).
Future<File> that completes
with a File for the copied file.
newPath identifies an existing file, that file is
removed first. If
newPath identifies an existing directory, the
operation fails and the future completes with an exception.
Future<File> copy(String newPath);