Gradle Retrolambda - plugin that will automatically build your java or Android project with retrolambda, giving you lambda goodness on Java 6 or 7.
ProGuard rules for Gradle Retrolambda
Add the following lines to your ProGuard configuration proguard.cfg file in project.
-dontwarn java.lang.invoke.* -dontwarn **$$Lambda$*
For more information about Gradle Retrolambda please see the website.