Update nullability for Title and Comment properties

Removed nullable annotation from Title, making it non-nullable.
Changed Comment to be nullable with conditional compilation
support for nullable reference types.

EnvelopeGenerator.Domain/Entities/Envelope.cs

@@ -76,11 +76,14 @@ namespace EnvelopeGenerator.Domain.Entities
 #if nullable
         ?
 #endif
-            Title
-        { get; set; }
+            Title { get; set; }
 
         [Column("COMMENT", TypeName = "nvarchar(128)")]
-        public string Comment { get; set; }
+        public string
+#if nullable
+        ?
+#endif
+            Comment { get; set; }
 
         [Column("CONTRACT_TYPE")]
         public int? ContractType { get; set; }