Cannot insert the value NULL into column 'Description'. EF Core 5

Question

I am using Entity Framework Core and I have this model class:

public class ConstraintRule
{
    public int Id { get; set; }
    public bool Enabled { get; set; }
    public PlantFilterType PlantFilterType { get; set; }
    public DateTime? FromDate { get; set; }
    public DateTime? ToDate { get; set; }
    public string PowerplantIds { get; set; } 
    public string PowerplantTypes { get; set; } 
    public User User { get; set; }
    public DateTime CreationTime { get; set; }
    public string Description { get; set; }
    public int Priority { get; set; }
}

This is the code in the context related to ConstraintRule model:

 builder.Entity<ConstraintRule>(entity =>
        {
            entity.Property(e => e.Description).HasMaxLength(500);
            entity.Property(e => e.PowerplantIds).HasMaxLength(2000);
            entity.Property(e => e.PowerplantTypes).HasMaxLength(2000);
        });

Description is a nullable string, this is the code generated by migration (also PowerplantIds and PowerplantTypes have the same problem):

 migrationBuilder.AlterColumn<string>(
            name: "Description",
            table: "ConstraintRules",
            type: "nvarchar(500)",
            maxLength: 500,
            nullable: false,
            defaultValue: "",
            oldClrType: typeof(string),
            oldType: "nvarchar(500)",
            oldMaxLength: 500,
            oldNullable: true);

I get this error:

Cannot insert the value NULL into column 'Description'

Answer 1

The problem solved by changing string to string?:

public string? Description { get; set; }

The problem doesn't exist before updating to Dot NET core 5. This is a little confusing because string is a reference type and by default is nullable.

Edit: C# 8 introduced a new feature called nullable reference types (NRT), it's value is "annotations" by default (Non-nullable unless declared with ?). To disable this feature open csproj file and edit it:

 <PropertyGroup>  
 <Nullable>disable</Nullable>

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