Any sales finance company may purchase or acquire, or agree to purchase or acquire, from any seller any contract on such terms and conditions as may be agreed upon between them. Filing of the assignment, notice to the buyer of the assignment and any requirement that the holder maintain dominion over the payments or the motor vehicle if repossessed shall not be necessary to the validity of a written assignment of a contract as against creditors, subsequent purchasers, pledgees, mortgagees and lien claimants of the seller. Unless the buyer has notice of the assignment of his contract, payment thereunder made by the buyer to the last known holder of such contract shall be binding upon all subsequent holders.