I am getting closer, but I don't know how to fix it:
Expected a string for (S), not: nil is written to the terminal when "pdftex.map" is searched for with the find_map_file callback. Since I don't have a map file, I return nil (the documentation tells me: »You have to return nil if the file cannot be found.«) When I create an empty file 'pdftex.map', everything is fine, but I am not too keen to provide empty files to the user. Patrick (BTW: all LuaTeX 0.85 / Mac OS X 10.11.1)
