[EAK-540] Handled the configuration-less plugin setup

plugin/src/main/java/com/exadel/aem/toolkit/plugin/maven/PluginMojo.java

@@ -237,6 +237,7 @@ private void populateReferenceEntries(PluginSettings.Builder builder) {
                 .stream()
                 .filter(plugin -> PLUGIN_ARTIFACT_ID.equals(plugin.getArtifactId()))
                 .map(ConfigurationContainer::getConfiguration)
+                .filter(Xpp3Dom.class::isInstance)
                 .map(Xpp3Dom.class::cast)
                 .findFirst()
                 .orElse(null);