NullPointerException is thrown after calling openmap function in R (OpenStreetMap pkg)

Question

I was trying to use the openmap function of the OpenStreetMap package in R. In the simplest way it looked like this:

map<-openmap(c(50.12397,8.67843),c(8.67843,50.10362),zoom=6,type='osm')
plot(map)

I tried several other examples I found on the internet but always get the same error:

java.lang.NullPointerException
    at edu.cens.spatial.RTileController.getTileValues(RTileController.java:109)
    at sun.reflect.GeneratedMethodAccessor4.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at RJavaTools.invokeMethod(RJavaTools.java:386)
Error in osmtile(x%%nX, y, zoom, type) : could not obtain tile: 33 21 6

Apparently I couldn't find a post with the same issue, so I hope someone can help me find a solution for my problem.

Thanks!