Utilizing nullable reference types

[tmilnthorp]

Per #688

[tmilnthorp]

@angularsen I am not sure how to fix this build

[angularsen]

Well, the error says

CSC : error CS8630: Invalid 'nullable' value: 'Enable' for C# 7.3. Please use language version 'preview' or greater.

I'll try pushing a language version fix and see if it helps.

[angularsen]

It builds locally here, so must be environment specific.

[codecov-commenter]

Codecov Report

Merging #789 into master will decrease coverage by 0.01%.
The diff coverage is 56.80%.

@@            Coverage Diff             @@
##           master     #789      +/-   ##
==========================================
- Coverage   63.90%   63.89%   -0.02%     
==========================================
  Files         280      280              
  Lines       41691    41684       -7     
==========================================
- Hits        26641    26632       -9     
- Misses      15050    15052       +2     

Impacted Files	Coverage Δ
UnitsNet/CustomCode/Quantities/Length.extra.cs	86.51% <ø> (ø)
UnitsNet/CustomCode/Quantities/Mass.extra.cs	93.87% <ø> (ø)
UnitsNet/GeneratedCode/Quantity.g.cs	81.45% <ø> (ø)
...sNet/InternalHelpers/ReflectionBridgeExtensions.cs	46.15% <0.00%> (ø)
UnitsNet/QuantityFormatter.cs	96.55% <ø> (ø)
UnitsNet/UnitFormatter.cs	100.00% <ø> (ø)
...nitsNet/GeneratedCode/Quantities/Acceleration.g.cs	59.77% <50.00%> (ø)
...et/GeneratedCode/Quantities/AmountOfSubstance.g.cs	61.29% <50.00%> (ø)
...tsNet/GeneratedCode/Quantities/AmplitudeRatio.g.cs	50.84% <50.00%> (ø)
UnitsNet/GeneratedCode/Quantities/Angle.g.cs	60.27% <50.00%> (ø)
... and 104 more

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[angularsen]

Weird, I just upgraded to VS2019 image and it.. worked. I tried earlier and it.. well, didn't work :-) Maybe the appveyor images have been improved since then.

[tmilnthorp]

Glad it works! Everything ok to merge? I just did the main UnitsNet project for now. We can work on projects in parts.

I'm also guessing that component runtime doesn't support this.

[angularsen]

Release UnitsNet/4.62.0 · angularsen/UnitsNet