Nullable references makes use of method-attributes to signal if references should have been null-checked first before calling.

<PropertyGroup>
    <LangVersion>8.0</LangVersion>
    <Nullable>enable</Nullable>
</PropertyGroup>

The "funny" part is that LangVersion=8.0 is only fully supported for NetCoreApp3. And if targeting NetCoreApp3 then it is enabled by default.

But these features also works out of the box on older platforms:

• Async enumerables
• Index and Range support
• Default Implementations
• Nullable Annotations in first-party libraries.

But if you try to use other language features of C# 8.0 while targeting .NET Standard 2.0, all bets are off!