Request: genericBuild example that doesn't return null

  All of the examples of genericBuild I could find just seem to trace a message and return null. Would be nice to have a more practical use cases. I believe generic builds can return a `ComplexType` or an `Array<Field>`, so there should be examples for both, and there should be an example that uses a Const type param.

If I come up with anything I'll post it here