<!--- Please read this! Before opening a new issue, make sure to search for keywords in the issues filtered by the "regression" or "bug" label and verify the issue you're about to submit isn't a duplicate. If you are submitting an issue with a tap, please include: - account details - target details - entities selected with meltano select (if you have selected any entities), as the bug may be related to a specific entity - the full elt command you are running - full output of the meltano elt command. Logs can get pretty long, so you can add the full log as a snippet in the Meltano project and add a link in the issue. ---> ### What is the current *bug* behavior? _What is happening now?_ ### What is the expected *correct* behavior? _What should be happening?_ ### Steps to reproduce _How one can reproduce the issue?_ Trying to get `tap-adwords` to accept custom `primary_keys`. Follow https://meltano.com/plugins/extractors/adwords.html#primary-keys and set the variables in the meltano.yml file (pic of config below + pic of output for `meltano config tap-adwords list`), meltano still uses the default value instead of the custom ones. Next, set the env var as given in the same documentation. It throws a TypeError on the processing of the config (pic also below). ### Relevant logs and/or screenshots _Please use code blocks (\`\`\`) to format console output_ meltano config  printout of `meltano config tap-adwords list`  error from running `meltano elt ...` with the env var `TAP_ADWORDS_PRIMARY_KEYS`  ### Possible fixes _If you can, link to the line of code that might be responsible for the problem or suggest a fix_ If you change the type of the variable `primary_keys` from `hidden` to `object` in the `discovery.yml` everything works as expected! I tried this locally and it worked. ### Further regression test _Ensure we automatically catch similar issues in the future_ - [ ] Write additional adequate test cases and submit test results - [ ] Test results should be reviewed by a person from the team