'The default for an inheritable name is found on a parent.'

def default(self, block, name):

    if (name in self.inheritable_names):
        field = block.fields[name]
        ancestor = block.get_parent()
        if (ancestor and (ancestor.location.category == 'library_content') and self.has_default_value(name)):
            return super(InheritingFieldData, self).default(block, name)
        while (ancestor is not None):
            if field.is_set_on(ancestor):
                return field.read_json(ancestor)
            else:
                ancestor = ancestor.get_parent()
    return super(InheritingFieldData, self).default(block, name)
