我的应用具有应用内购买功能。我使用计费库：

def billing_version = "4.1.0"
implementation("com.android.billingclient:billing:$billing_version")
implementation("com.android.billingclient:billing-ktx:$billing_version")

我在Firebase中观察到，LG Nexus 5X（Android 8.1）的用户无法购买。他尝试了几次，但得到同样的问题：

Fatal Exception: java.lang.RuntimeException: Unable to start activity ComponentInfo{studio.yatoo.calendarwidget/com.android.billingclient.api.ProxyBillingActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.IntentSender android.app.PendingIntent.getIntentSender()' on a null object reference
   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2778)
   at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856)
   at android.app.ActivityThread.-wrap11()
   at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589)
   at android.os.Handler.dispatchMessage(Handler.java:106)
   at android.os.Looper.loop(Looper.java:164)
   at android.app.ActivityThread.main(ActivityThread.java:6494)
   at java.lang.reflect.Method.invoke(Method.java)
   at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)

Caused by java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.IntentSender android.app.PendingIntent.getIntentSender()' on a null object reference
   at com.android.billingclient.api.ProxyBillingActivity.onCreate(com.android.billingclient:billing@@4.1.0:11)
   at android.app.Activity.performCreate(Activity.java:7009)
   at android.app.Activity.performCreate(Activity.java:7000)
   at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1214)
   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2731)
   at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856)
   at android.app.ActivityThread.-wrap11()
   at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589)
   at android.os.Handler.dispatchMessage(Handler.java:106)
   at android.os.Looper.loop(Looper.java:164)
   at android.app.ActivityThread.main(ActivityThread.java:6494)
   at java.lang.reflect.Method.invoke(Method.java)
   at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)

所有其他用户都没有这个问题。只有LG Nexus 5X的用户。有人能帮忙吗，如何解决这个问题？