generate-lv2.sh: not found

[magnetophon]

I'm trying to update the NixOS package for DISTRHO-Ports to the latest commit, but I'm running into a build error:

distrho-ports-unstable> [542/638] Generating ports-juce5/TheFunction-lv2-bundle with a custom command
distrho-ports-unstable> FAILED: [code=127] ports-juce5/TheFunction.lv2
distrho-ports-unstable> /build/source/ports-juce5/../scripts/generate-lv2.sh /build/source/build/libs/lv2-ttl-generator/lv2_ttl_generator ports-juce5/TheFunction.lv2 /build/source/build/ports-juce5/TheFunction-lv2.so
distrho-ports-unstable> /bin/sh: /build/source/ports-juce5/../scripts/generate-lv2.sh: not found

As far as I can tell, that file exists.
Any ideas?

Here is the complete build output: https://gist.github.com/magnetophon/a07d741d10b3e2c5229de61644418302