PlantUmlService: Cannot invoke method validate() on null object

Configuration:

grails 2.2.0,
empty project with 3 Domain classes
uml-class-diagram:0.4.0

Error 500: Internal Server Error

URI
    /toy-grails-app/uml/draw
Class
    java.lang.NullPointerException
Message
    Cannot invoke method validate() on null object

Around line 53 of 
grails-app/plugins/uml-class-diagram-0.4.0/grails-app/services/
         grails/plugin/umlclassdiagram/PlantUmlService.groovy

50:     */
51:    private void drawPackages(packageMap, StringBuilder uml, configurationCommand) {
52:        packageMap.each { packageName, classMap ->
53:            if (!configurationCommand.packageFilter.validate(packageName))
54:                return
55:            uml.append('namespace ').append(packageName ?: '_').append(' {\n')
56:            classMap.each { className, propertiesMap ->

igorrosenberg / grails-plugin-uml-class-diagram

PlantUmlService: Cannot invoke method validate() on null object #7