When you added the com.android.support:multidex dependency you actually added some dependencies that collide with other dependencies.
I solved it by:
—————
1. searching for the class, in you case the “RequestWeakReference.class” (in AndroidStudio just hit Ctrl+N on Windows or CMD-O on Mac)
2. See which jar contains it – Android Studio will write it in the popup.
3. Exclude it from all builds, for example:
android {
configurations{
all*.exclude module: 'servlet-api'
}
}