Snippet generator sometimes produces incorrect snippets like:

checkout scm: [$class: 'GitSCM', branches: [[name: '*/master']], extensions: [<object of type hudson.plugins.git.extensions.impl.CleanCheckout>], userRemoteConfigs: [[credentialsId: '4db1f14a-c479-48af-a3ea-da676bc2b051', url: 'https://github.com/XXXXXX/XXXXXXXXXX.git']]]

Here the extensions: [<object of type hudson.plugins.git.extensions.impl.CleanCheckout>] doesn't look like a valid Groovy syntax.
I think if the object reference can't be generated (probably it can be) it should be made more explicit that this construct does not work.