For the purpose of this chapter a person shall be considered to be lawfully upon the private property of the owner of such dog when he is on such property in the performance of any duty imposed upon him by the laws of this state or by the laws of the United States or the postal laws and regulations of the United States, when reading meters, when delivering milk, when making repairs to any public utility or service upon said premises or when on such property upon the invitation, either expressed or implied, of the owner or lessee of such property.