NullPointerException in loadUrl

[Prefest2018]

Execuse me, I found a NPE of TintBrowser on an AVD of API 19, the trace log is here:

E/AndroidRuntime( 8740): FATAL EXCEPTION: main
E/AndroidRuntime( 8740): Process: org.tint, PID: 8740
E/AndroidRuntime( 8740): java.lang.NullPointerException
E/AndroidRuntime( 8740): 	at org.tint.ui.managers.BaseUIManager.loadUrl(BaseUIManager.java:518)
E/AndroidRuntime( 8740): 	at org.tint.ui.managers.BaseUIManager.loadUrl(BaseUIManager.java:170)
E/AndroidRuntime( 8740): 	at org.tint.ui.managers.BaseUIManager.loadHomePage(BaseUIManager.java:200)
E/AndroidRuntime( 8740): 	at org.tint.ui.managers.TabletUIManager.closeCurrentTab(TabletUIManager.java:209)
E/AndroidRuntime( 8740): 	at org.tint.ui.activities.TintBrowserActivity.onOptionsItemSelected(TintBrowserActivity.java:305)
E/AndroidRuntime( 8740): 	at android.app.Activity.onMenuItemSelected(Activity.java:2600)
E/AndroidRuntime( 8740): 	at com.android.internal.policy.impl.PhoneWindow.onMenuItemSelected(PhoneWindow.java:1012)
E/AndroidRuntime( 8740): 	at com.android.internal.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:742)
E/AndroidRuntime( 8740): 	at com.android.internal.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:152)
E/AndroidRuntime( 8740): 	at com.android.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:881)
E/AndroidRuntime( 8740): 	at com.android.internal.view.menu.ActionMenuView.invokeItem(ActionMenuView.java:546)
E/AndroidRuntime( 8740): 	at com.android.internal.view.menu.ActionMenuItemView.onClick(ActionMenuItemView.java:115)
E/AndroidRuntime( 8740): 	at android.view.View.performClick(View.java:4438)
E/AndroidRuntime( 8740): 	at android.view.View$PerformClick.run(View.java:18422)
E/AndroidRuntime( 8740): 	at android.os.Handler.handleCallback(Handler.java:733)
E/AndroidRuntime( 8740): 	at android.os.Handler.dispatchMessage(Handler.java:95)
E/AndroidRuntime( 8740): 	at android.os.Looper.loop(Looper.java:136)
E/AndroidRuntime( 8740): 	at android.app.ActivityThread.main(ActivityThread.java:5017)
E/AndroidRuntime( 8740): 	at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime( 8740): 	at java.lang.reflect.Method.invoke(Method.java:515)
E/AndroidRuntime( 8740): 	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
E/AndroidRuntime( 8740): 	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
E/AndroidRuntime( 8740): 	at dalvik.system.NativeStart.main(Native Method)

I guess it is related to preferences 'PREFERENCE_HOME_PAGE' and 'PREFERENCE_START_PAGE_LIMIT' preference, would you like to have a look? I can also provide the test cases to reproduces the bug if necessary.