Improve condition

[ngocnhan-tran1996]

This PR includes:

• Check this.producer before calling lock() to createOrGetProducer() and close method
• Modernize switch pattern
• Reduce else condition

[artembilan]

@ngocnhan-tran1996 ,
Thank you for contribution!
Looks like you are addressing the other PR : #2862. Can yo mention that then and other contributor know, so we all don’t spend time looking into duplication?

[artembilan]

Pulling locally for final review and merge...

[artembilan]

Merged as 33da2a6.

@ngocnhan-tran1996 ,

thank you for contribution; looking forward for more!

A couple remarks:

Why your fork is called spring-amqp-fork? Why it cannot be just spring-amqp in your repositories?
Please, make yourself familiar with this article to understand of the commit message importance: https://cbea.ms/git-commit/.
Plus, GitHub is able to turn the first commit of the PR to its description.
This way we can save some time for extra typing.

[artembilan]

This PR has also fixed #2861.

[ngocnhan-tran1996]

Thanks @artembilan

I have a private repository name spring-amqp for some examples related spring-amqp. So I will rename it.