JER object compared to JetResolutionScaleFactor in JECStack.py

[jdulemba]

In the lines specified in the link below is there a reason why the input jer object is compared to the JetResolutionScaleFactor type instead of the input jersf object? Is this just a bug or is there a reason for this when building the JECStack object?

https://github.com/CoffeaTeam/coffea/blob/master/coffea/jetmet_tools/JECStack.py#L84-L96