Users should be warned of missing script output

[hinerm]

Consider this modified greeting.py script:

# @String(label="Please enter your name",description="Name field") name
# @OUTPUT String greeting_missing

greeting = "Hello, " + name + "!"

When I run this from the script editor there's no apparent error message, log output or warning. The script just silently does nothing.

This could be confusing, especially in more complicated scripts.

[ctrueden]

This is a feature, not a bug. 😉 That is: null output values are common and the framework does not complain when they exist because it is annoying. That said, I have been thinking about extending the required property of parameters to outputs. Required outputs should not be null, so maybe complaining about them makes sense.

[hinerm]

Well, if a script has declared @OUTPUT values isn't there kind of an implicit contract that you are asking the framework to do something with those values? Especially in the case of something like a Dataset.

One possibility might be to punt to the output handler, where you look up the handler by output type and let them respond based on the actual value.

Also, the intent of this issue (which I think was not completely clear from my initial writeup) was that we may want to differentiate between null values and missing values (e.g. I have an @OUTPUT referencing a variable name that is undefined in my scripting environment). The latter case seems less ambiguous that something has gone wrong in programming/program state.

[ctrueden]

I do not believe JSR-223 can, in general, differentiate between null and missing.

And even if it could, I think this would be potentially confusing as well, and less convenient for developers: they might want to "null out" a value towards the end of a script. There would be no way to "clear" a variable for the purpose of having it be ignored.

The latter case seems less ambiguous that something has gone wrong in programming/program state.

Do you think it would be sufficient to issue a warning/error for null required outputs (which is the default), but be silent about null non-required ones?