String index out of range!

java.lang.StringIndexOutOfBoundsException: String index out of range: -1
My code looks like this
```
String url=urls.get(options_list.getSelectionModel().getSelectedIndex());
String filename = file.getAbsolutePath();
DownloadManager downloadManager = DownloadManager.getInstance();
DownloadMission mission = new DownloadMission(url,"",filename);
downloadManager.addMission(mission);
downloadManager.start();
```

Start by reproducing the exception from the provided snippet, checking the selected index returned by options_list and tracing the DownloadMission and DownloadManager entry points. The issue names no files or tests; done means identifying the failing assumption and confirming the reported download flow no longer raises StringIndexOutOfBoundsException.

Written by the indexing model from the issue text.