It shall be sufficient defense to this proceeding, if any defendant of record establishes that:
(1) The condition or conditions described in the petition do not exist at the time of trial; or
(2) The condition or conditions alleged in the petition have been caused by the wilful or grossly negligent acts of 1 or more of the petitioning tenants or members of his or their families or by other persons on the premises with his or their consent; or
(3) Such condition or conditions would have been corrected, were it not for the refusal by any petitioner to allow reasonable access.