No railroad company owning and operating, or operating, a railroad shall adopt or promulgate a rule or regulation for the government of its servants or employees, or make or enter into an agreement with a person engaged in or about to engage in its service, in which such employee in any manner promises or agrees to hold such company harmless on account of an injury he may receive by reason of accident to, breakage, defect, or insufficiency in the cars or machinery and attachments thereto belonging on cars owned, operated, or run by such company being defective.