NoClassDefFoundError: groovy.swing.SwingBuilder

When trying to clean up the dependencies in grails-console (
https://github.com/grails/grails-core), I get a java.lang.NoClassDefFoundError:
groovy.swing.SwingBuilder on compilation.

I was surprised, because I do not find any usage of this class in the
sources.

Looking at the sources of groovy-console (which is a dependency of
grails-console), I see that groovy.console.ui.Console exposes the
SwingBuilder class as a public property, without declaring groovy-swing as
an api dependency, and I wonder if this could be the cause for this
compilation error, or if I'm missing something else.