[web2py] JSONDecodeError: No JSON object could be decoded

[wwwgong]

Hi,
add 2 functinos in myapp/controller/default.py

@service.run
def concat(a,b):
    return a+b

@service.jsonrpc
def concat2(a,b):
    return a+b

test them using browser
1)
http://127.0.0.1:8000/myapp/default/call/run/concat?a=hello&b=world
--> return 'helloworld'

2)
http://127.0.0.1:8000/myapp/default/call/jsonrpc/concat2?a=hello&b=world
--> error
Traceback (most recent call last):
  File "gluon/restricted.py", line 192, in restricted
  File "C:/web2py/applications/myapp/controllers/default.py", line
100, in <module>
  File "gluon/globals.py", line 145, in <lambda>
  File "C:/web2py/applications/myapp/controllers/default.py", line 80,
in call
  File "gluon/tools.py", line 3937, in __call__
  File "gluon/tools.py", line 3776, in serve_jsonrpc
  File "gluon/contrib/simplejson/__init__.py", line 386, in loads
  File "gluon/contrib/simplejson/decoder.py", line 403, in decode
  File "gluon/contrib/simplejson/decoder.py", line 421, in raw_decode
JSONDecodeError: No JSON object could be decoded: line 1 column 0
(char 0)

I am able to run todoApp from web2py book, so json module should be
working, but why cannot I test jsonrpc this way in browser?

Thanks,
Wen