PythonBuiltinClass.getArity() fails with ClassCastException

[numberpi]

In PythonBuiltinClass.getArity() returns the call to getAttribute(__NEW__) PNone, because the shape has no such field:

@44f9dee3{"__doc__":Object@2,
"__qualname__":Object@1,
"__name__":Object@0
}

Trace:

Caused by: java.lang.ClassCastException: com.oracle.graal.python.builtins.objects.PNone cannot be cast to com.oracle.graal.python.builtins.objects.function.PythonCallable
    at com.oracle.graal.python.builtins.objects.type.PythonBuiltinClass.getArity(PythonBuiltinClass.java:69)

[timfel]

This is resolved.