JSONDecodeError when reading file

[kthr]

When I try to read a simple file (via sbcl kernel) such as this one, using the following code:

(with-open-file (stream "~/test.txt" :direction :input)
    (do ((line (read-line stream nil) 
                    (read-line stream nil)))
           ((null line))
         (print line)))

I get a JSONDecodeError. Here is a full stack trace:
stacktrace.txt

Any help is very much appreciated :)

[fredokun]

this ones looks suspiscious... For various reasons I am for the
moment using ipython 2.x but as soon as I can switch to jupyter
I will try to see what is the issue here.
(I may switch to a more bulletproofed json encoder).
Sorry about the inconvenience