Unless there's a really good reason to use Guava here, just write as:
```
ImmutableSortedSet.Builder<BlockDevice> blockDevices = ImmutableSortedSet.orderedBy(new Comparator...);
for (VirtualGuestBlockDevice blockDevice : virtualGuest.getVirtualGuestBlockDevices()) {
  blockDevices.add(new BlockDevice(input.getDevice(), input.getVirtualDiskImage().getCapacity());
}
return blockDevices.build();
```
It's just so much easier to read and understand ;-)