Added some more tests for JsonMatcher + refactored some code to use nullable

[StefH]

No description provided.

[codecov]

Codecov Report

Merging #770 (2827c23) into master (9b7e590) will decrease coverage by 0.01%.
The diff coverage is 90.37%.

@@            Coverage Diff             @@
##           master     #770      +/-   ##
==========================================
- Coverage   72.09%   72.07%   -0.02%     
==========================================
  Files         209      209              
  Lines        7209     7206       -3     
  Branches      745      745              
==========================================
- Hits         5197     5194       -3     
  Misses       1787     1787              
  Partials      225      225              

Impacted Files	Coverage Δ
src/WireMock.Net/Http/HttpResponseMessageHelper.cs	75.60% <75.75%> (ø)
src/WireMock.Net/Util/BodyParser.cs	95.23% <94.38%> (-0.05%)	⬇️
...Abstractions/Admin/Mappings/WebhookRequestModel.cs	100.00% <100.00%> (ø)
src/WireMock.Net/Matchers/JsonMatcher.cs	93.15% <100.00%> (-0.19%)	⬇️
src/WireMock.Net/Owin/Mappers/OwinRequestMapper.cs	97.95% <100.00%> (ø)
src/WireMock.Net/Util/BodyParserSettings.cs	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 9b7e590...2827c23. Read the comment docs.