The preview window is blank when there are no changes in the lock file. This can occur in either of the below scenarios:

1. Uninstalling a package has no effect since another package still depends on it.
2. A restore fails due to a missing package and the final result cannot be determined

The results are still shown in the output window, but for these scenarios there are no installs, uninstalls, or upgrades. A different message should be shown letting the user know why there are no actions.