DictField / ListField: how to pass dict / list as default?

[lafrech]

Since #154, default values must be passed in deserialized form for consistency with marshmallow 3.

One can't write this anymore:

list_field = ListField(IntField, default=list)

One must now write

from umongo.data_objects import List
list_field = ListField(IntField, default=List)

Not ideal.

Shall we still take default values in serialized form in umongo even if it is not consistent with marshmallow 3? Is there another way to cast the default value in these specific cases?

Edit: in fact, the workaround above doesn't work, so it is worse than not ideal, it is a blocker.