Android Studio + Volley = NoClassDefFound?
Exception java.lang.NoClassDefFoundError: com.google.android.gms.common.AccountPicker
Found the fix here.
Basically, open a command prompt (or terminal) and navigate to your project directory. Use the following command on Windows:
For Windows users: gradlew.bat clean
And for mac users type: ./gradlew clean
Then reload Android Studio and try again!