Unable to configure reportLevel in build.gradle

[TuominenSami]

The example in README.md
import com.github.spotbugs.snom.Confidence
import com.github.spotbugs.snom.Effort
spotbugs {
ignoreFailures = false
showStackTraces = true
showProgress = true
effort = Effort.DEFAULT
reportLevel = Confidence.DEFAULT

gives following error:

Cannot set the value of extension 'spotbugs' property 'reportLevel' of type com.github.spotbugs.snom.Confidence using an instance of type java.lang.Class.

I have this in my build.gradle:
plugins {
id 'java'
id 'com.github.spotbugs' version '6.0.11'