Cannot resolve symbol errors for java primitives and Groovy

When calling the GDK extension methods on primitive types, Intellij warns that it cannot resolve the symbol:

However, the autocomplete sees the method and the test passes:

The widget java class:

public class Widget {
    float width = 1.1f;
}

Version info:

IntelliJ IDEA 2017.1.2
Build #IU-171.4249.39, built on April 25, 2017
JRE: 1.8.0_112-release-736-b16 x86_64
JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
Mac OS X 10.12.4
Groovy: 2.4.6