'Given a storage group name, get its parent storage group, if any.
:param serial_number: the array serial number
:param storagegroup_name: the name of the storage group
:returns: the parent storage group name, or None'

def get_parent_sg_from_child(self, serial_number, storagegroup_name):

    parent_sg_name = None
    storagegroup = self.rest.get_storage_group(serial_number, storagegroup_name)
    if (storagegroup and storagegroup.get('parent_storage_group')):
        parent_sg_name = storagegroup['parent_storage_group'][0]
    return parent_sg_name
