We were getting an IllegalArgumentException during channel creation on
some Samsung phones. Stack trace didn't give me much more than that, so
just adding in some additional safeguards that make sense based on
reading AOSP.
We manually play the ringtone when in-thread notifications are enabled,
but we weren't using the sound specified by the channel in the system
settings. This fixes that problem by reading the NotificationChannel
setting.
When using notification channels, us setting priority actually has
no effect. So instead of having a non-functional setting, we've
routed the notification priority setting to go to the system
notification channel settings page for our Messages channel.
