Added default constructor

While not strictly necessary for our needs, this is generally expected for exceptions, and recommended by Visual Studio's Code Analysis.

Author: JeremyCaney

Ignia.Topics/Repositories/TopicRepositoryException.cs

@@ -29,6 +29,12 @@ public class TopicRepositoryException : DbException {
     /*==========================================================================================================================
     | CONSTRUCTOR: TAXONOMY DELETE EVENT ARGS
     \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <summary>
+    ///   Initializes a new <see cref="TopicRepositoryException" /> instance.
+    /// </summary>
+    /// <param name="message">The message to display for this exception.</param>
+    public TopicRepositoryException() : base() { }
+
     /// <summary>
     ///   Initializes a new <see cref="TopicRepositoryException" /> instance with a specific error message.
     /// </summary>