NIFI-8761 Enable not setting a value for Escape Character in CSVReade…

[timeabarna]

…r controller service
https://issues.apache.org/jira/browse/NIFI-8761

Description of PR

Enables to use CSVReader and CSVRecordSetWriter without escape character

In order to streamline the review of the contribution we ask you
to ensure the following steps have been taken:

For all changes:

• Is there a JIRA ticket associated with this PR? Is it referenced
  in the commit message?

• Does your PR title start with NIFI-XXXX where XXXX is the JIRA number you are trying to resolve? Pay particular attention to the hyphen "-" character.

• Has your PR been rebased against the latest commit within the target branch (typically main)?

• Is your initial contribution a single, squashed commit? Additional commits in response to PR reviewer feedback should be made on this branch and pushed to allow change tracking. Do not squash or use --force when pushing to allow for clean monitoring of changes.

For code changes:

• Have you ensured that the full suite of tests is executed via mvn -Pcontrib-check clean install at the root nifi folder?
• Have you written or updated unit tests to verify your changes?
• Have you verified that the full build is successful on JDK 8?
• Have you verified that the full build is successful on JDK 11?
• If adding new dependencies to the code, are these dependencies licensed in a way that is compatible for inclusion under ASF 2.0?
• If applicable, have you updated the LICENSE file, including the main LICENSE file under nifi-assembly?
• If applicable, have you updated the NOTICE file, including the main NOTICE file found under nifi-assembly?
• If adding new Properties, have you added .displayName in addition to .name (programmatic access) for each of the new properties?

For documentation related changes:

• Have you ensured that format looks appropriate for the output in which it is rendered?

Note:

Please ensure that once the PR is submitted, you check GitHub Actions CI for build issues and submit an update to your PR as soon as possible.

[pvillard31]

Had a very quick look, looks good to me. Made a quick suggestion. Maybe @pgyori might also want to double check this pull request.

[timeabarna]

Thanks @pvillard31 for your help, applied your recommendation.

[pgyori]

It looks good to me, I only left a minor comment for a suggested name change.
The code looks good.
Tested the functionality and it works as expected.
The documentation is updated correctly and is understandable.
All the newly added code is carefully surrounded with unit tests. Great job!

I found some behavior that is not caused by this modification, but came up for me while testing this. If the input data is:
"abc\def"
and the escape character is not specified (null), I found that in the output we get:
"abc\\def"
It is present in earlier versions of NiFi, and occurs when we select e.g. RFC 4180 as the CSV Format (in the Reader). I think it might be something that is worth fixing since I suppose it is just a side-effect of having to escape backslashes in strings in Java. I'm not sure though, if it should be handled in this PR or a separate one. @timeabarna , @pvillard31 what do you think?

[pgyori]

Amending my previous comment:
"abc\def" turned into "abc\\def" because I was using JSONRecordSetWriter, and in JSON it is normal to escape the backslash. When using CSVRecordSetWriter with CSVReader, the "issue" does not occur, so it is fine, no bug to fix there.

[timeabarna]

Thanks @pgyori for your help, I've renamed the validator based on your recommendation.

[pgyori]

Thank you @timeabarna !
LGTM +1

[adenes]

Thanks @timeabarna for the contribution and @pgyori for the review. Merging to main.