Referencing a theme or plugin that does not exist explodes in horrible warnings.

[nickbreen]

... but it otherwise harmless.

tar (child): /var/www/v3.1.5: Cannot open: No such file or directory
tar (child): Error is not recoverable: exiting now
tar: Child returned status 2
tar: Error is not recoverable: exiting now
Unpacking the package...
Installing the theme...
Warning: The package could not be installed. The theme is missing the <code>style.css</code> stylesheet.
Theme update failed.
Success: Translations updates are not needed for the 'English (US)' locale.
PHP Warning:  unlink(/var/www/v3.1.5): No such file or directory in /usr/local/share/php/SCM_Command.php on line 140
Warning: unlink(/var/www/v3.1.5): No such file or directory in /usr/local/share/php/SCM_Command.php on line 140

Also happens when the GitHub Personal Access Token is invalid (tokens are automatically invalidated if they are accidentally checked in!).