abstract method causing undefined symbol ImportError

[mw66]

in my source/system.d I have:

class ClassAdapter {
  abstract Field process(Field old);
}

I was able to build the .so file, but under Python, when import:

>>> import mylib
ImportError: mylib.so: undefined symbol: _D6system12ClassAdapter7processMFCQBg5FieldZQl

Change the func to a null impl worked:

  /*abstract*/ Field process(Field old) {return null;};