public static bool AnyEmpty(params string[] args) => args.Any(x => string.IsNullOrWhiteSpace(x));

Example usage:

var networkPath = ConfigurationManager.AppSettings["IfsUncPath"];
var userName = ConfigurationManager.AppSettings["IfsUserName"];
var password = ConfigurationManager.AppSettings["IfsPassword"];
if (AnyEmpty(networkPath, userName, password))
	throw new Exception("AS400 IFS connection not configured");