[Libreoffice] Build error in helpcontent2

Hello,

i'm trying to build libreoffice from git but it gives me an error in 
helpcontent2:

Entering /home/rm/src/libo/helpcontent2/source/auxiliary

echo aux_langdirs:=en-US > ../../unxlngi6.pro/inc/aux_langs.mk
echo help_exist:=en-US > ../../unxlngi6.pro/inc/help_exist.mk
rm -f ../../unxlngi6.pro/bin/helpimg.ilst
/usr/bin/perl ../../helpers/create_ilst.pl 
-dir=/home/rm/src/libo/default_images/res/helpimg > 
../../unxlngi6.pro/bin/helpimg.ilst.unxlngi6.pro
Cannot find /home/rm/src/libo/default_images/res/helpimg.

create_ilst.pl -dir=directory [-pre=string]
-dir  root directory for the help images to
    be searched (default=current dir)
    Only *.png will be found.
-pre  define directory prefix (default=helpimg)


dmake:  Error code 2, while making '../../unxlngi6.pro/bin/helpimg.ilst'

ls -l /home/rm/src/libo/default_images
ls: cannot access /home/rm/src/libo/default_images: No such file or 
directory

This is the autogen line:

./autogen.sh --without-junit --without-java --disable-epm --disable-gtk 
--disable-gtk3 --disable-odk --disable-vba --disable-mozilla 
--disable-gstreamer --disable-randr --without-ppds --without-afms 
--disable-cairo-canvas --disable-neon --disable-dbus --disable-systray 
--disable-mathmldtd  --disable-extension-integration --with-system-libs 
--without-system-libvisio --without-system-libcmis 
--without-system-libwpd --without-system-cppunit --without-system-libwps 
--without-system-libwpg --without-system-graphite 
--without-system-sampleicc --without-system-redland 
--without-system-hunspell --without-system-mythes 
--without-system-altlinuxhyph --without-system-lpsolve 
--without-system-libexttextcat --without-system-poppler 
--host=i486-linux-gnu

thanks in advance,
riccardo