NullPointerException

[deive]

The request producer call returned a blank response (which isn't correct) but that causes the whole app to crash:

java.lang.NullPointerException: Attempt to invoke interface method 'java.util.Set java.util.Map.keySet()' on a null object reference
at com.realexpayments.hpp.HPPManagerFragment.getHPPPostData(HPPManagerFragment.java:283)
at com.realexpayments.hpp.HPPManagerFragment.success(HPPManagerFragment.java:269)
at com.realexpayments.hpp.HPPManagerFragment.success(HPPManagerFragment.java:59)
at retrofit.CallbackRunnable$1.run(CallbackRunnable.java:45)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7656)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)