NoneType has no len() error.

[dbt-labs]

NoneType has no len() error.

[joshuaLW]

@jtcohen6 good shout. I've just tried emptying the packages.yml then running dbt clean and i'm getting the errors i expected eg. "model x depends on y" so i'll keep going with cleaning up my models till all dependancies are removed... and hopefully it was just that... :) FWIW I thought dbt clean would have cleaned my packages.yml too... but computers can't read my mind can they?

[jtcohen6]

Hey @joshuaLW, this is indeed a cryptic error. The question of removing the Snowplow package seems like a good place to start debugging.

• Do you have anything else in packages.yml?
• Do you still have references to the snowplow package in dbt_project.yml?

[joshuaLW]

@jtcohen6 three things... I never actually checked that the snowplow modules were removed from packages.yml when i ran "dbt clean" but now having reversed these changes with "dbt deps" I've only this in that file:
packages:

• package: fishtown-analytics/snowplow
  version: 0.11.0

I did comment out all variables and models referencing the snowplow package in the project.yml

I didn't remove all dependencies upon snowplow from my models but i expected to get an error of the kind model x refers to model y that does not exist.

I'm going to go at it that way now actually: i'm going to remove references to snowplow models in my models first and then try removing snowplow module again.

[jtcohen6]

I did comment out all variables and models referencing the snowplow package in the project.yml

If I had to pick one of the three as the likeliest cause, I'd say it's this one. Try removing snowplow from packages.yml, run dbt clean, leave the vars in place, and then see what error you get back. (I hope it will be of the missing-ref kind.)

[joshuaLW]

@jtcohen6 So the plot thickens: the error returns even with packages.yml empty. It seems to be connected to one of the models I pinched from the package.
so to recap:

1. i installed snowplow with dbt deps
2. copied three models from the module into my models
3. cleared packages.yml of its content
4. ran dbt clean
5. dbt docs generate (any other cmd get's the same result) and i get the "object of type 'NoneType' has no len()"

[joshuaLW]

@jtcohen6 yup i found the line that was causing the problem. It was a reference to a variable that was nested in the package i'd removed.

[jtcohen6]

There it is! Well found.

I think it would be an improvement to the snowplow package if its models handled better the case when var('snowplow:pass_through_columns') is undefined in the project (None), rather than merely empty ([]).

Perhaps by rewriting that line to be:

{% if var('snowplow_pass_through_columns', []) | length > 0 %}

That way, if you do want to copy-paste the model code into your own project, and (sensibly) remove the snowplow-specific vars from your project config, you won't be stymied by a cryptic error.

I'm going to transfer this issue to the snowplow package repository, since that's where the change should take place.