java.lang.NullPointerException: Null reference used for synchronization (monitor-enter)

[kengleong]

FATAL EXCEPTION: main
Process: com.wokelchords.app.auctionhero, PID: 8207
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.wokelchords.app.auctionhero/com.vijay.jsonwizard.activities.JsonFormActivity}: java.lang.NullPointerException: Null reference used for synchronization (monitor-enter)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.NullPointerException: Null reference used for synchronization (monitor-enter)
at com.vijay.jsonwizard.activities.JsonFormActivity.getStep(JsonFormActivity.java:54)
at com.vijay.jsonwizard.fragments.JsonFormFragment.getStep(JsonFormFragment.java:162)
at com.vijay.jsonwizard.presenters.JsonFormFragmentPresenter.addFormElements(JsonFormFragmentPresenter.java:43)
at com.vijay.jsonwizard.fragments.JsonFormFragment.onViewCreated(JsonFormFragment.java:69)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1086)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1248)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1613)
at android.support.v4.app.FragmentController.execPendingActions(FragmentController.java:330)
at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:547)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1220)
at android.app.Activity.performStart(Activity.java:5949)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2261)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360) 
at android.app.ActivityThread.access$800(ActivityThread.java:144) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:135) 
at android.app.ActivityThread.main(ActivityThread.java:5221) 
at java.lang.reflect.Method.invoke(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:372) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694) 

I am running with
compileSdkVersion 23
buildToolsVersion "23.0.2"

Got an error when trying to implement the library.

java.lang.IllegalStateException: This Activity already has an action bar supplied by the window decor. Do not request Window.FEATURE_SUPPORT_ACTION_BAR and set windowActionBar to false in your theme to use a Toolbar instead.

Therefore i added this line in AndroidManifest.xml

<activity
    android:name="com.vijay.jsonwizard.activities.JsonFormActivity"
    android:theme="@style/Theme.AppCompat.Light.NoActionBar">
</activity>