XbimRect3D Union method looks wrong

[Hafplo]

https://github.com/xBimTeam/XbimEssentials/blob/4b42fdcef7eb8291fd8eefa5defc9ac58527e998/Xbim.Common/Geometry/XbimRect3D.cs#L387

I assume this method functionality is to create a unified BoundingBox (or Rect3D) from 2 smaller entities. However is it implemented without "this" and also returns "void". I have tested it, it seems to have no effect and cannot produce new variables.