ThreeTen Android Backport – is an adaptation of the JSR-310 backport for Android.
This library places the timezone information as a standard Android asset and provides a custom loader for parsing it efficiently.
ProGuard rules for ThreeTen Android Backport
Add the following lines to your ProGuard configuration proguard.cfg file in project.
# ThreeTen Android Backport -dontwarn sun.util.calendar.*
For more information about please see ThreeTen Android Backport website.