F-Droid fails to uninstall apps installed by other app stores

This comment:

java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference
	at org.fdroid.fdroid.installer.Installer.getUninstallScreen(Installer.java:146)
	at org.fdroid.fdroid.AppDetails2.uninstallApk(AppDetails2.java:771)
	at org.fdroid.fdroid.views.AppDetailsRecyclerViewAdapter$3.onClick(AppDetailsRecyclerViewAdapter.java:1075)
	at android.view.View.performClick(View.java:5657)
	at android.view.View$PerformClick.run(View.java:22453)
	at android.os.Handler.handleCallback(Handler.java:751)
	at android.os.Handler.dispatchMessage(Handler.java:95)
	at android.os.Looper.loop(Looper.java:154)
	at android.app.ActivityThread.main(ActivityThread.java:6236)
	at java.lang.reflect.Method.invoke(Native Method)
	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:891)
	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:781)

user comments:

v1.1-alpha3

Uninstalling an app not installed by f-droid

v1.1-alpha3

Trying to uninstall an app (open launcher) installed by another store.

v1.0.3

Trying to uninstall an app that has no version with compatible signature in the repository