Marshmallow post_load returns UnmarshalResult

[PabloAlexandre]

When Marshmallow Schema deserializes, the decorator @post_load returns a model with value. We use this model to access some attributes directly:

result = schema.loads()
print(result.attr)

Sometimes, when marshmallow lib version is incompatible with the project marshmallow version, the @post_load returns an UnmarshallResult object instead of the model value.

marshmallow-code/marshmallow#830

To fix this, we need to use result.data.attr instead of access directly the model attributes. This is a workaround, but the ideal scenario is @post_load always returns the Model instance.