New optional Foreign Key triggers Exception when querying

Question

Hello there!
I ran into an issue that I don't understand, therefore here I am.

Here is my model:

public class Property : FullAuditedEntity<Guid>, IMayHaveTenant  
    {  
        public int? TenantId { get; set; }  
  
        [Required]  
        [StringLength(PropertyConsts.MaxNameLength, MinimumLength = PropertyConsts.MinNameLength)]  
        public virtual string Name { get; set; }  
  
        [Required]  
        public virtual Guid AddressId { get; set; }  
  
        [ForeignKey("AddressId")]  
        public Address AddressFk { get; set; }  
  
        public virtual Guid GridId { get; set; }  
  
        [ForeignKey("GridId")]  
        public Grid GridFk { get; set; }  
    }  

I added the last part about GridId today and created a migration for it. Here it is:

migrationBuilder.AddColumn<Guid>(  
                name: "GridId",  
                table: "Properties",  
                type: "uniqueidentifier",  
                nullable: true,  
                defaultValue: null);  
  
  
migrationBuilder.AddForeignKey(  
                    name: "FK_Properties_Grids_GridId",  
                    table: "Properties",  
                    column: "GridId",  
                    principalTable: "Grids",  
                    principalColumn: "Id",  
                    onDelete: ReferentialAction.NoAction);  

Migration went well and the foreign key was created.
But now, when seeding my database, the following query triggers an error:

Property prop2 = _context.Properties.IgnoreQueryFilters().FirstOrDefault(p => p.Name == propertyName);  

And the error is:
System.Data.SqlTypes.SqlNullValueException : 'Data is Null. This method or property cannot be called on Null values.'

à Microsoft.Data.SqlClient.SqlBuffer.ThrowIfNull()  
   à Microsoft.Data.SqlClient.SqlBuffer.get_Guid()  
   à Microsoft.Data.SqlClient.SqlDataReader.GetGuid(Int32 i)  
   à Microsoft.EntityFrameworkCore.Query.Internal.SingleQueryingEnumerable`1.Enumerator.MoveNext()  
   à System.Linq.Enumerable.TryGetSingle[TSource](IEnumerable`1 source, Boolean& found)  
   à Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.Execute[TResult](Expression query)  
   à Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.Execute[TResult](Expression expression)  
   à System.Linq.Queryable.FirstOrDefault[TSource](IQueryable`1 source, Expression`1 predicate)  

As I understand, the new column is somehow expected to hold a value, even though it is defined as nullable.
Does someone understand what it's all about?