Questione giuridica chiave
Whether the 2007 official-form notice constituted a rent increase requiring formal justification and nullity review.
Decisione estratta
No. The prior relationship was still based on the original rent of CHF 18,000; the notice was an offer to accept CHF 16,000 from 1 August 2007, i.e. a debt remission, not a rent increase.
Motivazione estratta
The cantonal findings established the parties' true and concordant intent: the contractual rent remained CHF 18,000, while the landlords only temporarily waived part of their claims. Such temporary waivers are debt remissions under Art. 115 CO and do not require official-form reasons.