I did some analysis and have a question.

1. for Z14/Implementation: we now show the user underneath the field of the target function Z14K1 a message "Function is empty. Please select one" when Z14K1 is not filled. But this Z14K1 is an empty reference Z9K1. So if we would implement the above. Do we show both warnings or do we get rid of the specific warning for implementation. It is more specific so more useful. Or do we let the implementation message take precedence?
2. Same goes for a tester function and the tester call and tester result validation.

I am going to assume the specific errors take precedence and will keep track of those using a validatedPaths array.

Another thing I noticed. currently it clears errors when the publish dialog is closed (cancelled). Which we should probable change right. Otherwise if you close the dialog, you do not see which fields had empty values

Change #1189253 had a related patch set uploaded (by Daphne Smit; author: Daphne Smit):

[mediawiki/extensions/WikiLambda@master] Add pre-submission validation for empty Z9K1 references

https://gerrit.wikimedia.org/r/1189253

Current solution is not successfully keeping the Wikifunctions-Debug warning in the publish dialog.
Tested on converter page, where I can set some empty references and the code editor:

Change #1189253 merged by jenkins-bot:

[mediawiki/extensions/WikiLambda@master] Add pre-submission validation for empty Z9K1 references

https://gerrit.wikimedia.org/r/1189253

Tested on wikifunctions.org and confirmed it works as expected