Fix when no "SENT-BY" defined, get SentBy will throw exception (ical-…

…org#669)

* Fix when no "SENT-BY" defined, get SentBy will throw exception

* Enable nullable reference types and add Journal3 test.

Nullable reference types were enabled in the `Organizer` class, ensuring properties like `SentBy`, `DirectoryEntry`, and `Value` handle nullability appropriately. A new `Journal3` ICS file and its associated test were added to validate `SENT-BY` behavior in journals.

---------

Co-authored-by: Fei Xu <fei.xu@infoflosolutions.com>

Ical.Net.Tests/Calendars/Journal/JOURNAL3.ics

@@ -0,0 +1,24 @@
+BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//ABC Corporation//NONSGML My Product//EN
+BEGIN:VJOURNAL
+DTSTAMP:19970324T120000Z
+UID:uid5@host1.com
+ORGANIZER;SENT-BY=;CN=JohnSmith;DIR="ldap://host.com:6666/
+ o=3DDC%20Associates,c=3DUS??(cn=3DJohn%20Smith)":MAILTO:jsmith@host.com
+STATUS:FINAL
+CLASS:PRIVATE
+CATEGORY:Project Report, XYZ, Weekly Meeting
+DESCRIPTION:Project xyz Review Meeting Minutes\n
+ Agenda\n1. Review of project version 1.0 requirements.\n2.
+ Definition of project processes.\n3. Review of project schedule.\n
+ Participants: John Smith, Jane Doe, Jim Dandy\n-It was
+  decided that the requirements need to be signed off by
+  product marketing.\n-Project processes were accepted.\n
+ -Project schedule needs to account for scheduled holidays
+  and employee vacation time. Check with HR for specific
+  dates.\n-New schedule will be distributed by Friday.\n-
+ Next weeks meeting is cancelled. No meeting until 3/23.
+SUMMARY:Project xyz Review Meeting
+END:VJOURNAL
+END:VCALENDAR

Ical.Net.Tests/IcsFiles.cs

@@ -82,6 +82,7 @@ internal static string ReadStream(string manifestResource)
     internal static string HourlyUntil1 => ReadStream("Ical.Net.Tests.Calendars.Recurrence.HourlyUntil1.ics");
     internal static string Journal1 => ReadStream("Ical.Net.Tests.Calendars.Journal.JOURNAL1.ics");
     internal static string Journal2 => ReadStream("Ical.Net.Tests.Calendars.Journal.JOURNAL2.ics");
+    internal static string Journal3 => ReadStream("Ical.Net.Tests.Calendars.Journal.JOURNAL3.ics");
     internal static string Language1 => ReadStream("Ical.Net.Tests.Calendars.Serialization.Language1.ics");
     internal static string Language2 => ReadStream("Ical.Net.Tests.Calendars.Serialization.Language2.ics");
     internal static string Language3 => ReadStream("Ical.Net.Tests.Calendars.Serialization.Language3.ics");
@@ -168,4 +169,4 @@ internal static string ReadStream(string manifestResource)
 
     internal static string LibicalIcalrecurTest => ReadStream("Ical.Net.Tests.contrib.libical.icalrecur_test.out");
 
-}
+}

Ical.Net.Tests/JournalTest.cs

@@ -69,4 +69,15 @@ public void Journal2()
             Assert.That(j.Start, Is.Null);
         });
     }
-}
+
+    [Test, Category("Journal")]
+    public void Journal3()
+    {
+        var iCal = Calendar.Load(IcsFiles.Journal3);
+        ProgramTest.TestCal(iCal);
+        Assert.That(iCal.Journals, Has.Count.EqualTo(1));
+        var j = iCal.Journals.First();
+
+        Assert.That(j.Organizer.SentBy, Is.Null, "Expected Organizer's SENT-BY to be null, but it was not.");
+    }
+}

Ical.Net/DataTypes/Organizer.cs

@@ -3,6 +3,7 @@
 // Licensed under the MIT license.
 //
 
+#nullable enable
 using System;
 using System.Diagnostics;
 using System.IO;
@@ -16,9 +17,17 @@ namespace Ical.Net.DataTypes;
 [DebuggerDisplay("{Value}")]
 public class Organizer : EncodableDataType
 {
-    public virtual Uri SentBy
+    public virtual Uri? SentBy
     {
-        get => new Uri(Parameters.Get("SENT-BY"));
+        get
+        {
+            string sentBy = Parameters.Get("SENT-BY");
+            if (!string.IsNullOrWhiteSpace(sentBy))
+            {
+                return new Uri(sentBy);
+            }
+            return null;
+        }
         set
         {
             if (value != null)
@@ -27,7 +36,7 @@ public virtual Uri SentBy
             }
             else
             {
-                Parameters.Set("SENT-BY", (string) null);
+                Parameters.Remove("SENT-BY");
             }
         }
     }
@@ -38,9 +47,18 @@ public virtual string CommonName
         set => Parameters.Set("CN", value);
     }
 
-    public virtual Uri DirectoryEntry
+    public virtual Uri? DirectoryEntry
     {
-        get => new Uri(Parameters.Get("DIR"));
+        get
+        {
+            string dir = Parameters.Get("DIR");
+            if (!string.IsNullOrWhiteSpace(dir))
+            {
+                return new Uri(dir);
+            }
+
+            return null;
+        }
         set
         {
             if (value != null)
@@ -49,12 +67,12 @@ public virtual Uri DirectoryEntry
             }
             else
             {
-                Parameters.Set("DIR", (string) null);
+                Parameters.Remove("DIR");
             }
         }
     }
 
-    public virtual Uri Value { get; set; }
+    public virtual Uri? Value { get; set; }
 
     public Organizer() { }
 
@@ -71,7 +89,7 @@ public Organizer(string value) : this()
 
     protected bool Equals(Organizer other) => Equals(Value, other.Value);
 
-    public override bool Equals(object obj)
+    public override bool Equals(object? obj)
     {
         if (ReferenceEquals(null, obj))
         {
@@ -100,4 +118,4 @@ public override void CopyFrom(ICopyable obj)
             Value = o.Value;
         }
     }
-}
+}