```
$ mkdir test; cd test; rm; dir
Exception in thread "main" java.lang.NullPointerException
	at ru.fizteh.fivt.students.visamsonov.shell.Utils.stringArrayJoin(Utils.java:10)
	at ru.fizteh.fivt.students.visamsonov.shell.CommandDir.evaluate(CommandDir.java:12)
	at ru.fizteh.fivt.students.visamsonov.shell.Shell.parse(Shell.java:17)
	at ru.fizteh.fivt.students.visamsonov.shell.Shell.interactiveMode(Shell.java:34)
	at ru.fizteh.fivt.students.visamsonov.shell.Shell.main(Shell.java:41)
```