Solution to Value cannot be null. (Parameter 'source') Error in production

Question

I  got the following error in production Value cannot be null. (Parameter 'source')

My enum values are

public enum Offer{
  
    None=1,
    all,
    stop,

   
}

Class Emp{

   [Column(TypeName = "jsonb")]
   public list<Offer> offer { get; set; }

    public D d { get; set }

  public string FullName { get; set }

}

class D
{
   
   public string age { get; set }

   public string countryCode { get; set }

} 

public async Task<List<Emp>> ListEmp( List<Offer> offer ){

var query= catalogDb.Emp.Include(a=>a.D) .Where(a=>a.Name="xyz") .AsQueryable();

}

if(offer.Count>0){

                var result=query.AsEnumerable()
                                .Where(y => y.Offers.Any(z => offer.Contains(z)))
                                .ToList();
                return result;
            }

return await query.ToListAsync();

}

when I run  dotnet publish and   dotnet publish -c Release -o out then i run  dotnet out/Emp.dll

then i got 

   Unhandled exception. System.ArgumentNullException: String reference not set to an instance of a String. (Parameter 's')
   at System.Text.Encoding.GetBytes(String s)

could you pleas help me to solved this