Invalid Nullable Value – Enable for C# 7.3
I was playing around with Visual Studio 2019 and the open source ASP.NET Core blog engine Miniblog.Core. I cloned it to my local, opened it in Visual Studio 2019 and tried to build the solution. I immediately ran into the error below:
Error CS8630 Invalid 'nullable' value: 'Enable' for C# 7.3. Please use language version '8.0' or greater.
So, I looked up the error message and every Stack Overflow page I ended up on, says that I have to set the Language Version in Visual Studio. Okay, so how do I do that? I eventually found this answer, which gives you the steps to get to the Advanced Build Settings dialog box for the project.
- Right-click YourProject, click Properties
- Click Build if it's not already selected
- Change Configuration to All Configurations
- Click Advanced...
- Change the language version
When the dialog box showed up however, it didn't give me an option to set the Language Version.
The solution I ended up with involved manually editing the project file and adding an entry for the Language Version. So, I opened up the Miniblog.Core.csproj file and added
<LangVersion>preview</LangVersion> under the
<PropertyGroup> settings. It looks like this: