When calling:
InterstitialConfig config = new InterstitialConfig();

this exception is thrown in the latest Native Android SDK

10-03 16:04:32.874 11001-11097/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.mycompany, PID: 11001
java.lang.AbstractMethodError: abstract method not implemented
at com.appnext.core.Configuration.a(Configuration.java)
at com.appnext.core.Configuration.<init>(Configuration.java:24)
at com.appnext.ads.interstitial.InterstitialConfig.<init>(InterstitialConfig.java:16)