No, natural flavors cannot be zero. You don't list "natural flavors" if there are zero "natural flavors". It has to be 2 or more to be plural within the context of an ingredients label.
"NATURAL FLAVOR
A Natual Flavor is a flavor that is derived from a natural substance such as a fruit or fruit juice, spice, vegetable or herb. The term natural favor is defined by the FDA and all of PepsiCo’s flavors meet this definition."
https://www.pepsicobeveragefacts.com/home/ingredientglossary#NATURAL FLAVOR