Changed NullableContextOptions to work from msbuild variable 'CSharp8Nullable'.
MODIFY
Directory.Build.props
Directory.Build.props
<Project>
<PropertyGroup>
- <NullableContextOptions>enable</NullableContextOptions>
+ <NullableContextOptions>$(CSharp8Nullable)</NullableContextOptions>
</PropertyGroup>
</Project>
\ No newline at end of file

Changed NullableContextOptions to work from msbuild variable 'CSharp8Nullable'.