Should we create getters for the properties that enforce checking existence? It would ensure users dont assume a property like price always exists. Something like getPrice(feed) -> (bool, int64), it could return (exists, value). It's an alternative to storing the type as Option<Option<PropertyType>>.

There are chances that user can ignore the exist flag. Plus returning a bool will consume more gas.

As it stands they would have to first call hasPrice before using the price, which to me sounds like a greater chance of being missed by implementors since they would have to know about that method and intentionally use it. On the other hand, the exists flag more clearly signals the possibility that the field may not exist, and one would have to acknowledge this to ignore it. But that's just my opinion

They can just call getPrice(). It will return an error if price is zero.