Nonsense example class:

public class Bug
{
	public Object getObject()
	{
		return null;
	}
	
	public void bug()
	{
		Object obj=getObject();
		if (obj==null)
		{
			switch ("abc")
			{
			case "abc":
				break;
			default:
				throw new AssertionError();
			}
		}
		
		if (obj==null)	// (*)
		{
			getClass();
		}
	}
}


NetBeans reports an "Unnecessary test for null" hint at the line marked as (*), however this hint is wrong.
Of course in this nonsense code you instantly ask why I have two if statements for the same test, but in real life you might have other code between them.

Anyway, if I remove the line
throw new AssertionError();
then the false alarm warning disappears, so obviously NetBeans fails to see that there is a path through the "if (obj==null)" branch that does *not* throw an AssertionError. I'd guess there is no designated treatment of switch statements with breaks while checking whether this warning needs to be displayed.