Groovy is an extension to Java.
You may get this error if you are trying to
toString() an XML thing in Groovy, which annoyingly might also occur within an exception block,
making it exceptionally difficult to track this error down.
If using Gradle, you need to either use the
groovy-all dependency, or include the
implementation "org.apache.groovy:groovy-jsr223:$groovyVersion" implementation "org.apache.groovy:groovy-xml:$groovyVersion" // for XmlUtil
Note that this won’t work in Java 11+ because of module shenanigans. Only Groovy 4+ supports Java 11’s modules.