No contract for an easement of right-of-way for a pipeline, power or telephone line, sewer, main or similar works shall contain any provision which purports to exempt the corporation erecting, laying or installing the same from liability for injuries sustained by any person or property by reason of the laying, constructing, maintaining, operating, repairing, altering, replacing or removal of, or any failure or defect in, such line, sewer, main or works. Any such provision in any such contract is hereby declared to be against public policy and shall be null and void and unenforceable; provided, that this provision shall not apply as to any cause of action arising prior to June 26, 1964.