Skipping empty config sections without throwing exceptions

[RodionovDmitry]

This fixes NLog/NLog#5469

When config file has empty sections like this

{
  "NLog": {
    "throwConfigExceptions": true,
    "variables": {},
    "extensions": [],
    "targets": {},
    "rules": []
  }
}

Those sections are read as key-value pairs with null as the value.
This causes an exception when LoggingConfigurationParser is trying to parse it. There is a whitelist of properties allowed in the config.
The exception message is also a bit misleading
Unrecognized value 'targets'='' for element 'NLog'

In this PR I am checking if the "property" (which is actually an empty section) has no value. And if so - I am skipping it.

Added a test that blows up with exact same exception as the one described in the linked issue (before my changes). The test passes with the changes.
I had to add a dependency to Microsoft.Extensions.Configuration.Json to be able to pass JSON config as a string. But this is for the test project only, so I hope it is OK.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 94.73684% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 81.18%. Comparing base (ce05f3b) to head (c0c2f78).
Report is 2 commits behind head on master.

Files	Patch %	Lines
...ensions.Logging/Config/NLogLoggingConfiguration.cs	94.73%	0 Missing and 1 partial ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #724      +/-   ##
==========================================
- Coverage   81.21%   81.18%   -0.03%     
==========================================
  Files          19       19              
  Lines        1735     1743       +8     
  Branches      304      311       +7     
==========================================
+ Hits         1409     1415       +6     
+ Misses        189      188       -1     
- Partials      137      140       +3     

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[snakefoot]

Thank you for the pull-request, and starting the idea-race.

I guess it would work against the validation of unrecognized configuration-keys, as users might get confused why settings goes completely under the radar (ignored). Also curious what would happen with {myValue: null}, will it assign null or just skip the value?

Maybe the handling of simple-values assigned to null from JSON-config also needs to be tested (Unrelated to this bug).

[RodionovDmitry]

Thank you for the pull-request, and starting the idea-race.

I guess it would work against the validation of unrecognized configuration-keys, as users might get confused why settings goes completely under the radar (ignored). Also curious what would happen with {myValue: null}, will it assign null or just skip the value?

Maybe the handling of simple-values assigned to null from JSON-config also needs to be tested (Unrelated to this bug).

You have a valid concern :)
I added a separate test that proves that unknown simple keys still cause an exception if they are initialized with an explicit null value.

[snakefoot]

Think it looks great. And thank you for the unit-tests.

[snakefoot]

Are you in a hurry and need a release right now? or are you fine with waiting ?

[RodionovDmitry]

Are you in a hurry and need a release right now? or are you fine with waiting ?

No hurry at all 😄

This PR was a coding interview task for me 😄

Thanks for you time and guidance here @snakefoot 🙏

[snakefoot]

NLog.Extensions.Logging v5.3.9 has been released, that allows official sections like targets and variables to be empty.

Thanks again for the contribution.