What is the common law common law defense in an unlawful detainer action?

Applying this "persuasive reasoning" to our own state (Schweiger, supra, 3 Cal.3d at p. 513, 90 Cal.Rptr. 729, 476 P.2d 97), we chose "to recognize in unlawful detainer actions a defense that the eviction is sought in retaliation for the exercise of statutory rights by the tenant." (Id. at p. 517, 90 Cal.Rptr. 729, 476 P.2d 97.) We later commented that the substance of this common-law defense was codified in section 1942.5 (Barela v. Superior Court (1981) 30 Cal.3d 244, 249, 178 Cal.Rptr. 618, 636 P.2d 582), which had been enacted prior to Schweiger but did not become effective until the following year. (Schweiger, supra, 3 Cal.3d at p. 516, fn. 4, 90 Cal.Rptr. 729, 476 P.2d 97.)