Error when filters are empty

[romeerez]

Thank you for the polyfill!
Just a minor bug, when filters doesn't match it fails with cannot use .map of undefined, while in normal browser works fine

context-filter-polyfill/src/utils/filter.utils.ts

Line 11 in 17e4a91

.map(filter => filter.match(/([-a-z]+)(?:\((.*)\))?/i).slice(1, 3) as [AvailableFilter, string])

Wondering how typescript could compile this?