get_readonly_fields does not have proper obj

[ppython]

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The get_readonly_fields of a nested inline does not have the proper obj passed:

Consider the following configuration:

class SecondLevelInline(NestedStackedInline):
    model = SecondLevelModel

    def get_readonly_fields(self, request, obj=None):
        # obj is a "FirstLevelModel" instead of a "SecondLevelModel"


class FirstLevelInline(NestedStackedInline):
    model = FirstLevelModel
    inlines = [SecondLevelInline, ]

So i cannot make a conditional readonly_fields for my SecondLevelModel and I should have access to an instance of a SecondLevelModel.