A note for the documentation or maybe even a fix.
Being that until is a reserved word in Ruby, you one cannot make an api call like
api.get_course_list(since: ..., until: ...)
it must be
api.get_course_list(since: ..., _until: ...)
I guess that Swagger does this.
If one looks at the code though it is unnecessary and is just a artifact of the code generator.