Error uploading private app: undefined method `join' for nil:NilClass

I had the exact same issue when testing out the React scaffold package. I believe this boilerplate is somewhat raw and error-prone, and it hasn't been updated for a while, so I would advise against using it.

The error itself was related to the invalid format of the logo PNG files in the assets folder, if I recall correctly. I'm not sure what the exact issue was with these files, but when I replaced them with other PNG files, the app started building properly.  However, the error `undefined method `join' for nil:NilClass`doesn't contain useful info about the source of the error, so it would be a good idea for Zendesk to improve error handling here. 

Hello,

Thanks for the reply, but I was able to fix my issue. In the end, the problem was with damaged screenshot files. 

Best,
Andriy

Hey Nick and Andriy, apologies for the delay in my response!

Would you be able to provide your manifests for me so that I can see if there's anything funny going on? If you can do that, please strip out any sensitive data before posting. I'm not aware of any changes that would have affected the ability to upload apps, but I also trust that you both have done this enough times that something must have happened on our end. For what it's worth, I am able to install apps using the current version of ZCLI and in the UI, so hopefully it's just a minor issue!

Same story. I have a custom template, and the app was building fine. It just stopped working today. The build files look okay, and I can run the app locally with ?zcli_apps=true. But I can't import the private app to my instance or upload it to the marketplace.