[Bug] error 500 with adding an empty file in Observables of an Alert

### Request Type
Bug

### Problem Description
Error with curl command: 
```
{"type":"org.thp.scalligraph.InvalidFormatAttributeError","message":"Invalid format for artifacts.data: FString(file;inode/x-empty), expected filename;contentType;base64value ()"}% 
```

the pb seems to be related to Split function.