Merge "Fix missing computeIfAbsent() method in L_MR1 and M" am: db1ebc265c am: feaad2df13

Original change: https://android-review.googlesource.com/c/platform/packages/apps/Messaging/+/1341554

Change-Id: Iaccb9a0bfe078bb3712c875e30877bd2e0bdf1d2