Android Build Error - The Crashlytics build ID is missing

Hello,

Recently I faced a very strange issue in one of my android app. We were using Fabric IO for crash analytics earlier in the app and since now it's already merged with Firebase Analytics. we need to update the app. 

I removed Firebase maven repository and removed all plugins from build gradle file and removed Fabric code from everywhere. And build was successful. After that I followed all the instructions on getting started page of Firebase and crash analytics and build was successful.  And then problem started. Once we run the app, it crashes and shows following error in Logcat. 

"The Crashlytics build ID is missing. This occurs when Crashlytics tooling is absent from your app's build configuration. Please review Crashlytics onboarding instructions and ensure you have a valid Crashlytics account" 

Now it seems there is an issue with Firebase crash analytics account so I regenerated the google service json file add updated in project. But it didn't help. 

Searched on Google, answers suggest to put back Fabric plugin again in gradle file. Which does not make any sense to me. Since Fabric is out dated, why do we need to add it again. 

Finally after 2 days I was able to solve the problem. Here is the solution

Remove google service json file. Use Firebase assistant and connect with your account again. Select the project and it again generate google service json file. Keep link to fabric io repository in top level gradle file.

maven { url 'https://maven.fabric.io/public' }

I don't know how it worked but it works and I really don't know the reason of why it didn't work and why it started working after above solution. But it does solve the problem. 

If anyone who is reading this blog, knows the reason please put in comment.