What did the court decide in Green v. Superior Court?
Answered for: California
we have determined that the Hinson court properly recognized a common law implied warranty of habitability in residential leases in California, and we conclude that the breach of such warranty may be raised as a defense in an unlawful detainer action
California's Supreme Court adopted the implied warranty of habitability and allowed it as a defense in an eviction case. The sentence above is the court in its own words.
This answer is true in California and nowhere else on this site. Another jurisdiction is another answer, or an honest gap: see what has been read for California.