style: use string.Empty convention, add SP comments to FundModels

CertReports.Syncfusion/Models/FundModels.cs

@@ -1,9 +1,10 @@
 namespace CertReports.Syncfusion.Models;
 
+// SP: sfih_GetOptDettagli
 public class FundInfo
 {
-    public string Isin { get; set; } = "";
-    public string Strumento { get; set; } = "";
+    public string Isin { get; set; } = string.Empty;
+    public string Strumento { get; set; } = string.Empty;
     public string? Tipo { get; set; }
     public string? Societa { get; set; }
     public string? CategoriaMorningstar { get; set; }
@@ -48,6 +49,7 @@ public class FundReportData
     public bool ShowBranding { get; set; }
 }
 
+// SP: sfih_GetChartPrices
 public class FundChartPoint
 {
     public DateTime Date { get; set; }