`rpath` is configured even when not using `--bundle`

[topolarity]

seen on macOS by @ranjanan

rpath = nothing should correspond to... no rpath, not the default rpath

[KSepetanc]

In 0.2.3 rpath = nothing is now broken. It expects string. This worked in 0.2.2. It is also example API from tutorial.

ERROR: LoadError: MethodError: Cannot `convert` an object of type Nothing to an object of type String

The function `convert` exists, but no method is defined for this combination of argument types.

[gbaraldi]

Oh crap. That was a breaking change and should've been tagged as such