What is the ruling on paying Zakat al-Fitr in cash, and is it true that Omar bin Abdul Aziz paid it in cash?

Scholars have discussed the issue of giving money (value) in Zakat al-Fitr. Some permitted it, such as Abu Hanifa, and this is also the view of Al-Hasan al-Basri, Umar ibn Abd al-Aziz, and Al-Thawri. Others prohibited it, such as Malik, Ahmad, Ibn al-Mundhir, and Al-Shafi'i. Still others permitted it out of necessity, such as Ishaq and Abu Thawr.