Error running 'app': Unknown error in Android studio 3.1

I have updated my android studio to new stable version 3.1. After build project not able to run.

Let me know if anyone have face same issue or find any solution.

Just go to "Run/edit configurations.../" and scroll down to bottom of the window and here you see an option "Before launch..." First, remove whatever already inside the little window and then click on (+) icon and select "Gradle-aware Make" and then type "assembleDebug" and select the first option or that you need. This will solve your problem.