Removing Guava dependency

[neil1hart]

This PR upgrades the library to Java 8 and removes the Guava dependency.
(Fix issue #1082)
It is similar to PR #2086

The main reason is remove the transitive guava dependency for anything dependent on this library.

Incompatiblilites:
Updates from 1.7 to 1.8 as the minimum Java version. Rebase pulled in master's java change.
Public API changes where guava constructs have been exposed
Support for Guava Optional in API may have been lost.

What is missing:
I tried to limit the changed lines so there are many areas that can be cleaned up or refactored

• Cleanups (Predicates, Function can be written more compact with java 8)
• Duplicate code, like the replacement for Strings.nullToEmpty()

[codecov]

Codecov Report

Merging #2412 into master will decrease coverage by 0.09%.
The diff coverage is 94.76%.

@@             Coverage Diff             @@
##             master    #2412     +/-   ##
===========================================
- Coverage     95.08%   94.98%   -0.1%     
- Complexity     2989     3018     +29     
===========================================
  Files           339      339             
  Lines          7949     7956      +7     
  Branches        643      637      -6     
===========================================
- Hits           7558     7557      -1     
- Misses          251      253      +2     
- Partials        140      146      +6

[neil1hart]

I missed some needed changes that I commented out. Will get it updated by tonight.

[neil1hart]

org.reflections is breaking java 8 guava also. I'm looking at that also

[dilipkrish]

@neil1hart there is a PR for replacing reflections.

[dilipkrish]

BTW ❤️ the detailed incremental commits! Thank you for being taking the extra effort to make reviewing PRs easy!

[neil1hart]

Should I continue to look at increasing the coverage or is the slight decrease OK? I can't quite figure out where to add except maybe adding a test for guava Optional in a controller but need the Reflection replacement PR. I replaced the the guava Optional in BugsController with java.
I'll continue to rebase.

[dilipkrish]

@neil1hart don't think we need to chase down to that level, at some point it reaches diminishing returns. Im going to try and pull your change in, in the coming week or so. However, you may need to resolve conflicts from ongoing work in master.

[dilipkrish]

@neil1hart thank you very much for a very detailed and thorough PR. It made pulling it in so much easier!

[ArchangelX360]

@dilipkrish Hey, do we have a rough estimation when this will be published?

[dilipkrish]

Around september... mostly waiting on OAS 3.0 and #2056

[ArchangelX360]

Oh alright, do your best :). Thanks

[sourabhsparkala]

Hello All, I was wondering when are you planning for a release with this change? Please let me know.