Removed IsEmpty()

Since it's no longer possible to create a `Topic` without a `Key`, there isn't any need to retain `IsEmpty()`. (It also was almost never used.)

Author: JeremyCaney

Ignia.Topics.Tests/TopicTest.cs

@@ -34,18 +34,6 @@ public void Topic_CreateTest() {
       Assert.AreEqual<string>(topic.Attributes.GetValue("ContentType"), "ContentType");
     }
 
-    /*==========================================================================================================================
-    | TEST: IS EMPTY
-    \-------------------------------------------------------------------------------------------------------------------------*/
-    /// <summary>
-    ///   Creates a topic using the default constructor, and ensures it's returned as empty.
-    /// </summary>
-    [TestMethod]
-    public void Topic_IsEmptyTest() {
-      var topic = new Topic();
-      Assert.IsTrue(topic.IsEmpty);
-    }
-
     /*==========================================================================================================================
     | TEST: CHANGE ID
     \-------------------------------------------------------------------------------------------------------------------------*/

Ignia.Topics/Topic.cs

@@ -141,14 +141,6 @@ public Topic Parent {
     /// </summary>
     public TopicCollection Children { get; }
 
-    /*==========================================================================================================================
-    | PROPERTY: IS EMPTY
-    \-------------------------------------------------------------------------------------------------------------------------*/
-    /// <summary>
-    ///   Gets whether the Topic's Key is invalid (null or empty).
-    /// </summary>
-    public bool IsEmpty => String.IsNullOrEmpty(Key);
-
     /*==========================================================================================================================
     | PROPERTY: CONTENT TYPE
     \-------------------------------------------------------------------------------------------------------------------------*/