Hi, I did the following test (using a Button instead of a TextView, but that does not really matter):
in the Dominoes sample, in the initButton() method of GUIManager, right after the code that creates the "Clear" button,
I added the following code:
Typeface tf = Typeface.createFromAsset(mAppContext.getAssets(), "fonts/ariali.ttf");
Where mAppContext is just the context passed to the GUIManager in the GUIManager constructor (I store it in a private varaiable mAppContext)
and where ariali.ttf is a sample font that I downlaoded from internet and added to the "assets/fonts/" folder (same as you did);
the test shows that it works all right, the text on the button is actually rendered with italic arial (in my case) and no Null Pointer;
One thing to check: try maybe with a different font; also, make sure to understand if it is getAssets() returning NULL or the createFromAsset method;
finally, please note that the font name is CASE SENSITIVE (i.e. it might fail because of that, so double check your font name in your code).
I hope this helps.