You can test the behavior of the snippet generator in a following way:

• Create a new workflow project
• Select "Groovy CPS DSL" in Definition for Workflow
• Check "Snippet generator"
• Select "General Build Step" for "Sample Step"
• Select "Copy artifacts from another project" for "Build Step"
• Configure copyartifact, and click "Generate Groovy"

Result:

• The validation for "Project name" fails with NPE.
• The generated result is
  ```
  step <object of type hudson.plugins.copyartifact.CopyArtifact>
  ```