This is a fun side effect of ParallelStep not having a DataBoundConstructor - theoretically, it should be possible to have both parallel and other steps directly within a stage, but the attempt to validate the arguments to parallel goes wrong due to that missing DataBoundConstructor.

The ModelParser does look for parallel and treat it differently if it's the only step under the stage, but we're not looking for that in JSONParser at all, and we're not rejecting parallel in other cases in the first place. So...need to think about this some.