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Looks like the tests are failing:
@staticmethod
def test__validate_invalid():
class Mine(model.Model):
foo = model.StringProperty()

    prop = model.StructuredProperty(Mine)
    with pytest.raises(exceptions.BadValueError):

> prop._validate(None)

tests/unit/test_model.py:3013:

self = StructuredProperty(model_class=Mine), value = None

def _validate(self, value):
    if isinstance(value, dict):
        # A dict is assumed to be the result of a _to_dict() call.
        return self._model_class(**value)
    if not isinstance(value, self._model_class):
        raise exceptions.BadValueError(

> "In field {}, expected %s instance, got %s"
% (self._name, self._model_class.__name__, value.__class__)
)
E TypeError: not all arguments converted during string formatting