render_data.py

def render_data(self, obj):
    if isinstance(obj,dict):
        value = obj.get(self.id, None)
        if not value and 'fields' in obj: # added
            value = obj['fields'].get(self.id, None) # added
    else:
        value = getattr(obj,self.id, None)

    if callable(value):
        return self.format_data(value())
    else:
        return self.format_data(value)