Amy conveys (transfers) a plot of land to "Robert Lopez and his heirs as long as the land is used for charitable purposes." For forty years, Robert uses the land to generate income that he donates to various charities. After both Amy and Robert die (Amy died before Robert) and after Robert's death, his daughter Mary begins to keep the income from the property for herself Do Amy's heirs have any rights or entitlement to the plot of land? Explain