Set _text to null in Anchor if the body content is empty.

Previously it just left it to whatever it was set to before,
which was super confusing and impossible to debug.

beehive-netui-tags/src/main/java/org/apache/beehive/netui/tags/html/Anchor.java

@@ -325,6 +325,8 @@ public class Anchor extends AnchorBase
             bodyContent.clearBody();
             if (value.length() > 0)
                 _text = value;
+            else
+                _text = null;
         }
         return SKIP_BODY;
     }