Anne is an international student living in Brisbane during the Covid-19 virus lockdown. She is renting a room at $180 per week in rooming accommodation. She agreed to rent the room prior to the outbreak of the virus. After the virus starts to spread, Anne's landlord decides to provide an incentive to Anne to encourage Anne not to break her accommodation agreement. The landlord fears that Anne will return to her home country and that the landlord with not be able to relet the room during the virus outbreak. The landlord calls Anne and tells Anne "you can pay $90 per week rent from now, 1 July 2020, until the end of the year". At the end of the year the landlord is in financial hardship and decides to enforce the original agreement with Anne ($180 per week). The landlord tells Anne "I'm sorry. I know I promised that you could pay half rent but the legal agreement was for $180 per week. You owe me the arrears of $90 per week for the last six months". What argument could Ann raise to avoid having to pay the arrears? 5 POINTS