Image builder 19.07.9 fails in

I have been using image builder for years to build a custom image for the espressobin (mvebu). I am currently using 19.07.8 and I can build this fine right now.

I just tried to build 19.07.9 though and it fails with:

Traceback (most recent call last):
  File "/home/hamish/src/espresso-openwrt/openwrt-imagebuilder-19.07.9-mvebu-cortexa53.Linux-x86_64/scripts/", line 34, in <module>
    "source_date_epoch": int(getenv("SOURCE_DATE_EPOCH")),
ValueError: invalid literal for int() with base 10: ''
make[4]: *** [Makefile:117: /home/hamish/src/espresso-openwrt/openwrt-imagebuilder-19.07.9-mvebu-cortexa53.Linux-x86_64/build_dir/target-aarch64_cortex-a53_musl/json_info_files/openwrt-19.07.9-mvebu-cortexa53-globalscale_espressobin-squashfs-sdcard.img.gz.json] Error 1

Is this a known issue with a known solution?