I have often received similar, or the same, stack traces for a Nexus 5X …

Fatal Exception: java.lang.RuntimeException Unable to start activity ComponentInfo{com.xxxx.xxxx/com.google.android.gms.ads.NotificationHandlerActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference

.. soon after releasing a new version to the Google Play Store.

After a bit of Googling these Nexus 5X crash reports appear to be related to Google Play Store testing, for example https://issuetracker.google.com/issues/268432128.

I would just tend to ignore any reported crashes from a Nexus 5X. According to Wikipedia the Nexus 5X was discontinued in 2016 so these devices are unlikely to make up any significant percentage of the real app install base anyway.