I'm not 100% sure what transpired but the unless within exec types were resulting in CommandNotFoundException
This release fixes that issue by specifying the absolute path to the command within the unless attribute.
Example failures in debug mode were showing:
/Stage[main]/Jenkins_windows_agent/Nssm::Install[Jenkins_Agent]/Exec[install_service_name]/unless: nssm : The term 'nssm' is not recognized as the name of a cmdlet, function, script file, or operable program. Check
/Stage[main]/Jenkins_windows_agent/Nssm::Install[Jenkins_Agent]/Exec[install_service_name]/unless: the spelling of the name, or if a path was included, verify that the path is correct and try again.