Don't fallback to default (empty) package if the specified package doesn't exist.

[aaaaaa2493]

Example:

TestedProgram server1 = new TestedProgram("chat.server");
TestedProgram client1 = new TestedProgram("chat.client");

Will result in executing the same class if the user haven't created chat/server and chat/client packages and created just single main class because they both will fallback to the default package.