If a creditor of an insolvent estate who is in possession of any property belonging to that estate, to which he has a right of retention or over which he has a landlord's legal hypothec, delivers that property to the trustee of that estate, at the latter's request, he shall not thereby lose the security afforded him by his right of retention or lose his legal hypothec, if, when delivering the property, he notifies the trustee in writing of his rights and in due course proves his claim against the estate: Provided, that a right to retain any book or document of account which belongs to the insolvent estate or relates to the insolvent's affairs shall not afford any security or preference in connection with any claim against the estate.