Fix Version/s: None
The contract for `daf.butlerUtils.CameraMapping.parentSearch` states that `None` will be returned if no matches are found.
But in one of the options
` if os.path.realpath(pathPrefix) != os.path.realpath(root):`
the code says `return ` instead of `return None`.
This is then not caught properly by `daf.butlerUtils.mapping.map`, which was checking just for the return value `is not None`.
The behavior of parentSearch is clearly an error (it's againt the documentation for the function).
I would also suggest that `daf.butlerUtils.mapping.map` should check more robustly for `if newPath:` rather than `if newPath is not None:`.
Thus we explicitly set up this if/else to return `None` if `not paths` instead of ``.