I have a global list of mountains. I want to filter all French mountains. To do this, I need to check if iso3166_1Alpha2 is set to FR. The problem is that not all mountains have a value. The script dies after it hits a null value I think because this is the error:

Uncaught (in promise) TypeError: Cannot read properties of null (reading 'iso3166_1Alpha2')

This is my script. Seems my check of !== null is not working and do not know why.

function addJSON() {

  let url = "https://development.example.com/admin/mtn/json/mtn_areas.geojson";

  fetch(url)

    .then(function (response) {

      return response.json();

    })

    .then(function (data) {

      let mtn = data.features;

      for (var i = 0; i < mtn.length; i++) {

        if (mtn[i].properties.location.iso3166_1Alpha2 !== null) {

          x = mtn[i].properties.location.iso3166_1Alpha2;

          console.log(x);

        }

      }

    });

}