SecurityException: Failed to find provider null for user 0; on ActiveAndroid on Android 8.0

As pointed out by @GeigerGeek security changes on Android 26 and above require you to specify the content provider in your manifest.

For ActiveAndroid you can add the below to your Manifest and change your package name.

<provider
  android:name="com.activeandroid.content.ContentProvider"
  android:authorities="<your.package.name>"
  android:enabled="true"
  android:exported="false">
</provider>

If using flavours on your build process you can use below instead:

android:authorities="${applicationId}"

Using ${applicationId} will help in flavor based project structure where application package may be different for each flavors.

For more solutions or info this was taken from here.