[Feature][transform] Add a module to set default value for null field

[Interest1-wyt]

#1963

Purpose of this pull request

Set default value for null field

Check list

• Code changed are covered with tests, or it does not need tests for reason:
• If any new Jar binary package adding in your PR, please add License Notice according
  New License Guide
• If necessary, please update the documentation to describe the new feature. https://github.com/apache/incubator-seatunnel/tree/dev/docs

[ruanwenjun]

Please add an issue and describe why you need to add this transform plugin. In fact, I am confusion with the plugin name etl.

[Interest1-wyt]

I wanted to conceive an ETL plugin that contains various functions at first. The null field processing is only a small part of it. After your question, I found that the function of the module I defined was too general, and each plugin of setunnel must have its own Clear functionality, so I changed my code and module name, which now only provides null field handling. Also I have opened an issue for it.

After I commit new code,Dead Link Checker failed,It doesn't seem to be my problem. Can you help me rerun the ci

[ruanwenjun]

Generally looks good to me, It might be better if you can submit a PR to add e2e case for this plugin.

[ruanwenjun]

Please fix the scala checkstyle problem.

[Interest1-wyt]

OK, I will revise it and submit it later :)

[Interest1-wyt]

[Interest1-wyt]

Sorry, I accidentally clicked the close button, could you please help to restart the build :)

[Interest1-wyt]

Generally looks good to me, It might be better if you can submit a PR to add e2e case for this plugin.
I try to add a test case to the e2e module, but the error "Could not find a valid Docker environment" is displayed when I run it. Running other test methods in e2e also reports this error. Why is this and how can I fix it?
The project runs on the win10 operating system and the docker component is installed.

[Interest1-wyt]

Generally looks good to me, It might be better if you can submit a PR to add e2e case for this plugin.
I try to add a test case to the e2e module, but the error "Could not find a valid Docker environment" is displayed when I run it. Running other test methods in e2e also reports this error. Why is this and how can I fix it?
The project runs on the win10 operating system and the docker component is installed.

Sorry, this is a problem with my local docker installation, which has been solved.

[ruanwenjun]

LGTM