Espruino build package error

Hi,
I want to add a module to the Espruino system and load it on a Puck.js device. The module is written in C and has to be compiled and linked with Espruino.
For now, i just try to build Espruino, which i downloaded from GitHub, on a Linux machine (OpenSUSE 12.2). I run:

make clean;DFU_UPDATE_BUILD=1 BOARD=PUCKJS RELEASE=1 make

Compilation and link seams to be Ok in spite of minor warnings. The .lst .hex and .elf files are properly generated.
I get an error in the package generation:

...
GEN espruino_1v91.599_puckjs.lst
GEN espruino_1v91.599_puckjs.hex
Not merging softdevice or bootloader with application
# nrfutil  pkg generate --help
nrfutil pkg generate espruino_1v91.599_puckjs.zip --application espruino_1v91.599_puckjs.hex --application-version 0xff --hw-version 52 --sd-req 0x8C --key-file targets/nrf5x_dfu/dfu_private_key.pem
Traceback (most recent call last):
  File "/usr/local/bin/nrfutil", line 5, in <module>
    from pkg_resources import load_entry_point
  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 2735, in <module>
    working_set.require(__requires__)
  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 690, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 588, in resolve
    raise DistributionNotFound(req)
pkg_resources.DistributionNotFound: protobuf
make: *** [espruino_1v91.599_puckjs.hex] Erreur 1
make: *** Attente des tâches non terminées....

Do you have an idea on this problem ? Is there any software component missing ?
Thank you for your help.