Compiling CM12.1 for Z3C

As part of my learning process to use the CyanogenMod ports effort and spread the word, I need to compile CM12to get familiar with it.
However I am stuck at the $breakfast z3c step. I also extracted the blobs from an existing dogfood z3c device. Here is the error message I get :

$ breakfast z3c
including vendor/cm/
build/core/ *** _nic.PRODUCTS.[[device/sony/z3c/]]: “vendor/sony/msm8974-common/” does not exist. Stop.
Device z3c not found. Attempting to retrieve device repository from CyanogenMod Github (
Found repository: android_device_sony_z3c
Default revision: cm-12.1
Checking branch info
CyanogenMod/android_device_sony_z3c already exists
Syncing repository to retrieve project.
Fetching project CyanogenMod/android_device_sony_z3c
Fetching projects: 100% (1/1), done.

Repository synced!
Looking for dependencies
build/core/ *** _nic.PRODUCTS.[[device/sony/z3c/]]: “vendor/sony/msm8974-common/” does not exist. Stop.

** Don’t have a product spec for: ‘cm_z3c’
** Do you have the right repo manifest?

Should I extract them from an Android? I have installed TWRP but at the moment, I cannot directly flash a compiled CM12 from there it seems (I guess the partition layout is different)