I have the following defined in XML that was working with 2.5:

<Button class="btn">   
    <Button.formattedText>
        <FormattedString>
            <FormattedString.spans>
                <Span text=" Login"></Span>
            </FormattedString.spans>
        </FormattedString>
    </Button.formattedText>
</Button>  

This throws the following error:

An uncaught Exception occurred on "main" thread.
java.lang.NullPointerException: Attempt to invoke virtual method 'int android.graphics.Typeface.getStyle()' on a null object reference
at org.nativescript.widgets.CustomTypefaceSpan.applyCustomTypeFace(CustomTypefaceSpan.java:35)
at org.nativescript.widgets.CustomTypefaceSpan.updateDrawState(CustomTypefaceSpan.java:23)
at android.text.TextLine.handleRun(TextLine.java:932)
at android.text.TextLine.measureRun(TextLine.java:417)
at android.text.TextLine.measure(TextLine.java:296)
at android.text.TextLine.metrics(TextLine.java:270)
at android.text.BoringLayout.isBoring(BoringLayout.java:311)
at android.widget.TextView.makeSingleLayout(TextView.java:6715)
at android.widget.TextView.makeNewLayout(TextView.java:6610)
at android.widget.TextView.onMeasure(TextView.java:6961)
at android.view.View.measure(View.java:18788)
at org.nativescript.widgets.CommonLayoutParams.measureChild(CommonLayoutParams.java:262)
at org.nativescript.widgets.StackLayout.onMeasure(StackLayout.java:83)
at android.view.View.measure(View.java:18788)
at org.nativescript.widgets.CommonLayoutParams.measureChild(CommonLayoutParams.java:262)
at org.nativescript.widgets.StackLayout.onMeasure(StackLayout.java:83)
at android.view.View.measure(View.java:18788)
at org.nativescript.widgets.CommonLayoutParams.measureChild(CommonLayoutParams.java:262)
at org.nativescript.widgets.MeasureHelper.measureChildFixedColumnsAndRows(GridLayout.java:1059)
at org.nativescript.widgets.MeasureHelper.measure(GridLayout.java:869)
at org.nativescript.widgets.GridLayout.onMeasure(GridLayout.java:279)
at android.view.View.measure(View.java:18788)
at org.nativescript.widgets.CommonLayoutParams.measureChild(CommonLayoutParams.java:262)
at org.nativescript.widgets.ContentLayout.onMeasure(ContentLayout.java:32)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2643)
at android.view.View.measure(View.java:18788)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2100)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1216)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1452)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1107)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6013)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858)
at android.view.Choreographer.doCallbacks(Choreographer.java:670)
at android.view.Choreographer.doFrame(Choreographer.java:606)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

Also tried the short format - directly having FormattedString inside the button and then directly Span inside it. Also the same problem happens with Label. Before testing I have uninstalled the app from device and nuked node_modules and platforms.

EDIT
Seems related to the btn class from the nativescript theme. If that is removed the exception does not happen.