Can `metadataMap.get("jclouds-group")` return the empty string? If not, how about
```
String groupName = null;
...
groupName = metadataMap.get("jclouds-group"); // may be null
...
if (groupName == null) {
  groupName = nodeNamingConvention.groupInUniqueNameOrNull(from.getName());
}
...
```