Cleanup getInstance() references

[darinpope]

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your master branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests - that demonstrates feature works or fixes the issue

NOTE: The larger deletion in MailSender.java was due to spotbugs failing. Once the resulting code was in place, spotbugs was successful.

@alecharp @oleg-nenashev

[oleg-nenashev]

AFAICT in this case null checks are legitimate. Please use getInstanceOrNull