when the facetlist has not and EventTracker breaks the FaceList usage

[jairoFernandez]

Describe the bug 🐛
when the facetlist has not and EventTracker breaks the FaceList usage

To Reproduce 🔍
Steps to reproduce the behavior:

Just try to instanciate the object like this:

late final _facetList = _productsSearcher.buildFacetList(
    filterState: _filterState,
    attribute: 'activity_type',
  );

After that when you try to access to _facetList.facets the validation try to use the getters, because the property was marked as late final, the code break.

Expected behavior 💭
Should be work with that param in null

Environment:

• OS: MacOS Sonoma 14.2.1 (23C71)
• Library Version 1.0.0-pre

[jairoFernandez]

I hope this PR can be fix that one 🙏🏼 https://github.com/algolia/algoliasearch-helper-flutter/pull/123