Page showing "Null check operator used on a null value" on a red screen

Hi everyone,

I am trying to set a map which is pulling data from a firestore collection and showing the documents as markers. But, it shows this error screen:

Also, FYI there is only 1 document which has the "Location" field value set. Unfortunately, other users didn't provide their device location.
Below is the configuration of the map:

The objective is to show only those documents as markers which have the "phone_number" field non-empty.

I am open to other workarounds which I can use to implement this.

Need to resolve this ASAP.