Non-nullable property must contain a non-null value when exiting constructor. Consider declaring the property as nullable.

Recently, I was getting this warning for most of the properties which are not specified as nullable. I was not happy this warning, though I was able to run my .NET 6 application smoothly.

Exact Error:

Non-nullable property ‘propername’ must contain a non-nullvalue when exiting constructor. Consider declaring the property as nullable

After carefully observing this error message, it makes sense for those properties. In order to minimize the likelihood that our code causes the runtime to throw System.NullReferenceException, we need to resolve this warning.

Therefore, the compiler is giving warning in the solution that the default assignment of your properties (which is null) doesn’t match its state type (which is non-null string).

https://docs.microsoft.com/en-us/dotnet/csharp/nullable-references

We can resolve this error in 3 ways.

Solution 1

We can simply make the properties nullable, as shown below:

public class AppSetting {
    public string? ReferenceKey { get; set; }
    public string? Value { get; set; } 
    public string? Description { get; set; }
}

Solution 2

We can assign default value to those properties as shown below:

public class AppSetting {
    public string ReferenceKey { get; set; } = “Default Key”;
    public string Value { get; set; } = “Default Value”;
    public string Description { get; set; } = “Default Description”;
}

Alternatively, you can give a reasonable default value for non-nullable strings as string.empty.

Solution 3

You can disable this warning from project level. You can disable by removing the below line from project file csproj or setting. 

<Nullable>enable</Nullable>

Reference: https://docs.microsoft.com/en-us/dotnet/csharp/nullable-references#nullable-contexts

These are three ways you can overcome the above warning.

Kind Regards