In attempting to test my trytond service wit hthhis line

make check-system TESTS="trytond"

I get this errror

[...]
adding user 'guixbuilder08'...
adding user 'guixbuilder09'...
adding user 'guixbuilder10'...
adding user 'trytond'...
adding user 'postgres'...
registering public key
'/gnu/store/94y24as2zk3n3n39602vlanqb1g5j0c0-guix-0.13.0-12.0a154c1/share/guix/hydra.gnu.org.pub'...
ERROR: In procedure append:
ERROR: In procedure append: Wrong type argument in position 1 (expecting
empty list): "-c en_US.utf8"

Entering a new prompt.  Type `,bt' for a backtrace or `,q' to continue.
GNU Guile 2.2.2
Copyright (C) 1995-2017 Free Software Foundation, Inc.

Guile comes with ABSOLUTELY NO WARRANTY; for details type `,show w'.
This program is free software, and you are welcome to redistribute it
under certain conditions; type `,show c' for details.

Enter `,help' for help.
scheme@(guile-user)>


Where does this -c en_US.utf8 string come from ?
Where is append being called ?

Could I have a slighhtly more verbose error message ?

Thanks