Fix missing null checks

.editorconfig

@@ -127,6 +127,8 @@ csharp_space_between_method_call_empty_parameter_list_parentheses = false
 csharp_preserve_single_line_statements = true
 csharp_preserve_single_line_blocks = true
 csharp_style_namespace_declarations = file_scoped
+# Do not suggest primary constructor
+dotnet_diagnostic.IDE0290.severity = none
 
 ###############################
 # VB Coding Conventions       #

Calendare.VSyntaxReader.slnx

@@ -0,0 +1,5 @@
+<Solution>
+  <Project Path="VSyntaxReader.Examples/VSyntaxReader.Examples.csproj" />
+  <Project Path="VSyntaxReader.Tests/VSyntaxReader.Tests.csproj" />
+  <Project Path="VSyntaxReader/VSyntaxReader.csproj" />
+</Solution>

VSyntaxReader/Properties/DateTimeProperty.cs

@@ -81,7 +81,7 @@ public DeserializeResult Deserialize(ICalendarComponent calendarComponent)
 
     public string Serialize()
     {
-        return DateTimePropertyHelper.Serialize(Raw, DataType, DefaultDataType, [Value], IsValid);
+        return DateTimePropertyHelper.Serialize(Raw, DataType, DefaultDataType, Value is not null ? [Value] : [], IsValid);
     }
 
     public IProperty DeepClone() => Copy();

VSyntaxReader/Properties/FreeBusyProperty.cs

@@ -33,7 +33,7 @@ public FreeBusyProperty(CalendarObject calendarObject)
     public DeserializeResult Deserialize(ICalendarComponent calendarComponent)
     {
         Value = new CaldavFreeBusy();
-        List<string> values = [Raw.Value];
+        List<string> values = [];
         if (Raw.Value is not null)
         {
             values = [.. Raw.Value.Split(',')];

VSyntaxReader/Properties/RecurrenceDateProperty.cs

@@ -87,7 +87,7 @@ public DeserializeResult Deserialize(ICalendarComponent calendarComponent)
             return hasValidTimezone;
         }
 
-        List<string> values = [Raw.Value];
+        List<string> values = [];
         var deserializeResult = new DeserializeResult(true);
         if (Raw.Value is not null)
         {