title: JsonSerializer Struct with asp-net core 3.0
body: <p>I'm having issues with .net core 3.0 when I convert a struct to a json. (with wasn't a problem when I was using .net core 2.2)</p>
  
  <p>This is my struct</p>
  
  <pre><code>[Serializable]
  struct Item
  {
     public int A;
     public string B;
     public int C;
     public decimal D;
     public decimal E;
  }
  </code></pre>
  
  <p>This is my code</p>
  
  <pre><code>var linhas = COD_PRODUTO.Count;
  Item[] item = new Item[linhas];
  
  for (int cont = 0; cont &lt; linhas; cont++)
  {
     DESCRICAO = _context.Produtos.Where(c =&gt; c.COD_PRODUTO == COD_PRODUTO[cont]).Select(c =&gt; 
     c.DESCRICAO).Single().ToString();
  
     item[cont].A = COD_PRODUTO[cont];
     item[cont].B = DESCRICAO;
     item[cont].C = QUANTIDADE[cont];
     item[cont].D = PRECOUNITARIO[cont];
     item[cont].E = TOTAL[cont];
  }
  
  var json = JsonSerializer.Serialize(item); //3.0
  Debug.WriteLine("----------------------" + json);
  
  return new JsonResult(json);
  
  </code></pre>
  
  <p>It's returning me empty values, any help?</p>