jruby -Xnative.enabled=false -e 'File.atime("file:")'
SystemCallError: Unknown error - Unknown Error (0) - __UNKNOWN_CONSTANT__

The reason for this is we assume the FileResource generated will hit jnr-posix and when the stat fails it then asks jnr-posix for the errno(). EmptyFileResource will be generated in this case and it does not hit jnr-posix at all. One possible solution is to manually set errno from EmptyFileResource so that this pattern of depending on jnr-posix for error is valid?

Extra note that it is amazing this case works for me with enabled=true since it is still using EmptyFilerResource. The last errno set must just happen to be an enoent.