Austin Rental Properties (hereinafter, "Austin Rental") and Margie Williamson (hereinafter, "Williamson") enter into an agreement whereby Williamson would lease a building owned by Austin Rental for the purpose of operating a nightclub. Under the contract Williamson was required to make minimum monthly payments until the nightclub was ready to be opened for business and then the monthly payments would increase to a rate equal to four times the minimum monthly payments. The property is located in Travis County, Texas within the limits of the City of Austin. The lease was to run from January 1 2020 until December 31, 2021. The club was ready to open and Williamson notified Austin Rental of this fact on March 20, 2020. On March 24, 2020, "to prevent the further spread of the CoVID-19 virus," the City of Austin and Travis County, enacted ordinances requiring citizens to "shelter in place." While the original ordinances were for a relatively short period of time, there was discussion that in all likelihood the ordinance would be extended and in fact it was extended. According to the terms of the ordinance the operation of a nightclub was not deemed an "essential activity" and therefore Williamson would not be able to open the nightclub as planned. Williamson also expressed her concern that even if and when the "shelter in place" ordinance was rescinded, she did not feel comfortable in opening the nightclub because of the increase risk of spreading the disease. For all of those reasons, Williamson refused to make any payments due after March 24 and gave notice to Austin Rental that the contract was at an end. Based on the above, which concepts discussed in Chapter 18 might Williamson rely on to justify her actions. Discuss in detail each of the relevant concepts explaining how each might be applicable