Error with gr_modtool makexml howto_detect_ff

GNU Radio
1

I am working to make a detector block in gnuradio 3.6.5.1 using gr-how
“out-of-tree module”. I am stuck with an error during " gr_modtool
makexml howto_detect_ff " command.

GNU Radio module name identified: howto
Warning: This is an experimental feature. Don’t expect any magic.
Searching for matching files in lib/:
Making GRC bindings for lib/howto_detect_ff_impl.cc…
Traceback (most recent call last):
File “/usr/local/bin/gr_modtool”, line 41, in
main()
File “/usr/local/bin/gr_modtool”, line 37, in main
modtool.run()
File
“/usr/local/lib/python2.7/dist-packages/gnuradio/modtool/modtool_makexml.py”,
line 66, in run
(params, iosig, blockname) = self._parse_cc_h(f)
File
“/usr/local/lib/python2.7/dist-packages/gnuradio/modtool/modtool_makexml.py”,
line 157, in _parse_cc_h
return (parser.read_params(), parser.read_io_signature(), blockname)
File
“/usr/local/lib/python2.7/dist-packages/gnuradio/modtool/parser_cc_block.py”,
line 214, in read_params
params_list = _scan_param_list(make_match.end(0))
AttributeError: ‘NoneType’ object has no attribute ‘end’

Thanks in advance,
CHAABANE