Crashing on devices below SDK Version 19

[Sarun1001]

Hi, first of all thanks for this awesome lib.
Lib tend to crash on almost all emulators and devices below SDK 19. But working fine on latest devices.
Any idea ?...
Complete stacktrace...

E/AndroidRuntime: FATAL EXCEPTION: main
java.lang.NullPointerException
at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:465)
at android.view.View.measure(View.java:15172)
at it.beppi.balloonpopuplibrary.BalloonPopup.draw(BalloonPopup.java:255)
at it.beppi.balloonpopuplibrary.BalloonPopup.show(BalloonPopup.java:213)
at it.beppi.balloonpopuplibrary.BalloonPopup.access$400(BalloonPopup.java:35)
at it.beppi.balloonpopuplibrary.BalloonPopup$Builder.show(BalloonPopup.java:541)
at it.beppi.knoblibrary.Knob.displayBalloons(Knob.java:273)
at it.beppi.knoblibrary.Knob.onDraw(Knob.java:133)
at android.view.View.draw(View.java:13458)
at android.view.View.getDisplayList(View.java:12409)
at android.view.View.getDisplayList(View.java:12453)
at android.view.View.draw(View.java:13182)
at android.view.ViewGroup.drawChild(ViewGroup.java:2929)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2799)
at android.view.View.getDisplayList(View.java:12407)
at android.view.View.getDisplayList(View.java:12453)
at android.view.View.draw(View.java:13182)
at android.view.ViewGroup.drawChild(ViewGroup.java:2929)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2799)
at android.view.View.getDisplayList(View.java:12407)
at android.view.View.getDisplayList(View.java:12453)
at android.view.View.draw(View.java:13182)
at android.view.ViewGroup.drawChild(ViewGroup.java:2929)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2799)
at android.view.View.getDisplayList(View.java:12407)
at android.view.View.getDisplayList(View.java:12453)
at android.view.View.draw(View.java:13182)
at android.view.ViewGroup.drawChild(ViewGroup.java:2929)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2799)
at android.view.View.draw(View.java:13461)
at android.view.View.getDisplayList(View.java:12409)
at android.view.View.getDisplayList(View.java:12453)
at android.view.View.draw(View.java:13182)
at android.view.ViewGroup.drawChild(ViewGroup.java:2929)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2799)
at android.view.View.getDisplayList(View.java:12407)
at android.view.View.getDisplayList(View.java:12453)
at android.view.View.draw(View.java:13182)
at android.view.ViewGroup.drawChild(ViewGroup.java:2929)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2799)
at android.view.View.getDisplayList(View.java:12407)
at android.view.View.getDisplayList(View.java:12453)
at android.view.View.draw(View.java:13182)
at android.view.ViewGroup.drawChild(ViewGroup.java:2929)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2799)
at android.view.View.draw(View.java:13461)
at android.widget.FrameLayout.draw(FrameLayout.java:467)
at android.view.View.getDisplayList(View.java:12409)
at android.view.View.getDisplayList(View.java:12453)
at android.view.View.draw(View.java:13182)
at android.view.ViewGroup.drawChild(ViewGroup.java:2929)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2799)
at android.view.View.getDisplayList(View.java:12407)
at android.view.View.getDisplayList(View.java:12453)
at android.view.View.draw(View.java:13182)
at android.view.ViewGroup.drawChild(ViewGroup.java:2929)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2799)
at android.view.View.getDisplayList(View.java:12407)
at android.view.View.getDisplayList(View.java:12453)
at android.view.View.draw(View.java:13182)
at android.view.ViewGroup.drawChild(ViewGroup.java:2929)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2799)
at android.view.View.getDisplayList(View.java:12407)
at android.view.View.getDisplayList(View.java:12453)
at android.view.View.draw(View.java:13182)
at android.view.ViewGroup.drawChild(ViewGroup.java:2929)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2799)
at android.view.View.draw(View.java:13461)
at android.widget.FrameLayout.draw(FrameLayout.java:467)
at com.android.internal.policy.impl.PhoneWindow$DecorView.draw(PhoneWindow.java:2183)
at android.view.View.getDisplayList(View.java:12409)
at android.view.View.getDisplayList(View.java:12453)