Nullable fixes - nullability on Base

[adamhathcock]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 63.33333% with 11 lines in your changes missing coverage. Please review.

Project coverage is 66.26%. Comparing base (daec64c) to head (22880bd).
Report is 1 commits behind head on dev.

Files with missing lines	Patch %	Lines
...Speckle.Sdk/Api/GraphQL/Serializer/MapConverter.cs	0.00%	6 Missing and 1 partial ⚠️
src/Speckle.Sdk/Credentials/Account.cs	0.00%	1 Missing ⚠️
src/Speckle.Sdk/Credentials/AccountManager.cs	0.00%	1 Missing ⚠️
src/Speckle.Sdk/Host/Attributes.cs	0.00%	1 Missing ⚠️
...ckle.Sdk/Serialisation/V2/Send/ObjectSerializer.cs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##              dev     #184       +/-   ##
===========================================
+ Coverage   53.67%   66.26%   +12.59%     
===========================================
  Files         233      249       +16     
  Lines        9370    10014      +644     
  Branches     1074     1066        -8     
===========================================
+ Hits         5029     6636     +1607     
+ Misses       4087     3032     -1055     
- Partials      254      346       +92     

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