add nullable recurrence id

BeckmanComms.Api.DataTransferObjects/BeckmanComms.Api.DataTransferObjects.nuspec

@@ -11,6 +11,9 @@
     <description>Model classes for use with the Beckman Institute web API.</description>
     <summary>Model classes for use with the Beckman Institute web API.</summary>
     <releaseNotes>
+      unreleased:
+      * Add nullable EventDto recurrence ID.
+      
       2.0.0-alpha08:
       * Add group type property to GroupDto.
 

BeckmanComms.Api.DataTransferObjects/V2/Events/EventDto.cs

@@ -71,5 +71,10 @@ namespace BeckmanComms.Api.DataTransferObjects.V2.Events
         /// Whether event is recurring.
         /// </summary>
         public bool Recurring { get; set; }
+
+        /// <summary>
+        /// Shared identifier linking recurring events.
+        /// </summary>
+        public int? RecurrenceId { get; set; }
     }
 }
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