Search for "Walldorf(Hess)" on nominatim should return this place as "railway station" or "railway stop", corresponding to  
json$features$properties$category == "railway" & json$features$properties$type == "station" / "stop". 
Currently this search returns a place near Heidelberg which is a very bad match as the term "Walldorf(Hess)" is used in Deutsche Bahn's timetable info for this station. Check out www.bahn.de, Frankfurt Hbf to Mannheim Hbf.
Thanks for correcting, and thanks for all the great work on openstreetmap!