I ran into this issue using Android Studio 3.5.1. I was using a test device (Nexus 7… yeah, yeah. I know). I updated the ROM on it to Android 9.
When I tried running the very first app, it installed and ran fine. When I changed my name in “Hello World” I got an error when installing the application of “null”. I found a StackOverflow article about when deploying to older Android versions, you need to add some install flags so that it will allow testing and replace an already installed application.
Here’s the SO article: Installation failed due to: 'null' - Android Studio 3.5 - Stack Overflow
It wasn’t incredibly difficult to find the place to make that change, but if someone was new to development, finding that config page and changing that option would be really intimidating. Maybe cover that in a note?
Thanks for the book!