NullPointerException (etc) from Parcel.readException

NullPointerException (etc) from Parcel.readException

Exceptions that look like this are confusing:
FATAL EXCEPTION: main
java.lang.NullPointerException
at android.os.Parcel.readException(Parcel.java:1437)
at android.os.Parcel.readException(Parcel.java:1385)
at
com.yourpackage.ipc.IYourClass$Stub$Proxy.yourMethod(IYourClass.java:488)
at com.yourpackage.ipc.YourClassShim.yourMethod(YourClassShim.java:269)
I found a bunch of related questions for this, but none with the answer to
"how do you debug this". So I'm making this Question/Answer.
By looking at the android source here and here you'll see that it can be
throwing any of these (the NullPointerException is just what I had):
SecurityException(msg);
BadParcelableException(msg);
IllegalArgumentException(msg);
NullPointerException(msg);
IllegalStateException(msg);
RuntimeException("Unknown exception code: " + code + " msg " + msg);
But what's causing these?