IntelliJ cannot resolve symbol in build.sbt

In my case, after upgrading Intellij forgot that the project was a Scala project.

Delete .idea/ and import the project to fix this.

I looked on jetbrains' error tracker and found this is a known bug.

"Cannot resolve symbol project" in build.sbt

https://youtrack.jetbrains.com/issue/SCL-9512

To fix this issue, I imported: import sbt.project on top of my build.sbt

I am working with IntelliJ IDEA 16 EAP