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I'm making some assumptions here based on the code fragments you've given.
Here you are making a call to a static method in the IRC class. Presumably mc.thePlayer.username is a String which you pass to the main(String name) method.
This is not instantiating an object of the IRC class. You are accessing the class members (static methods and variables).
The Public IRC() constructor you posted earlier does not execute except when you create a new instance. Nothing you've given shows that you are creating a new instance.
If the constructor doesn't run, then the mc variable doesn't get set.
If the mc variable doesn't get set, you get a NullPointerException when you try to access its contents (which don't exist).
Try throwing a couple of debugging lines into the constructor:
That will tell you whether or not that constructor is being called or not.