Added missing serialVersionUIDs

src/main/java/com/sun/syndication/feed/opml/Attribute.java

@@ -28,6 +28,9 @@ import com.sun.syndication.feed.impl.ToStringBean;
  * @author <a href="mailto:cooper@screaming-penguin.com">Robert "kebernet" Cooper</a>
  */
 public class Attribute implements Cloneable, Serializable {
+
+	private static final long serialVersionUID = 1L;
+	
     private String _name;
     private String _value;
 

src/main/java/com/sun/syndication/feed/opml/Opml.java

@@ -29,6 +29,9 @@ import com.sun.syndication.feed.WireFeed;
  * @author <a href="mailto:cooper@screaming-penguin.com"> Robert "kebernet" Cooper</a>
  */
 public class Opml extends WireFeed {
+    
+    private static final long serialVersionUID = 1L;
+    
     private Date _created;
     private Date _modified;
     private Integer _verticalScrollState;

src/main/java/com/sun/syndication/feed/opml/Outline.java

@@ -33,6 +33,9 @@ import com.sun.syndication.feed.impl.ToStringBean;
  * @author <a href="mailto:cooper@screaming-penguin.com">Robert "kebernet" Cooper</a>
  */
 public class Outline implements Cloneable, Serializable {
+    
+    private static final long serialVersionUID = 1L;
+    
     private Date _created;
     private List _attributes;
     private List _categories;

src/main/java/com/sun/syndication/feed/synd/impl/ConverterForOPML10.java

@@ -346,6 +346,9 @@ public class ConverterForOPML10 implements Converter {
     }
 
     private static class TreeContext extends Stack {
+        
+        private static final long serialVersionUID = 1L;
+
         TreeContext() {
             super();
         }

src/main/java/com/sun/syndication/feed/synd/impl/TreeCategoryImpl.java

@@ -18,6 +18,8 @@ import com.sun.syndication.feed.synd.SyndCategoryImpl;
  */
 public class TreeCategoryImpl extends SyndCategoryImpl {
 
+    private static final long serialVersionUID = 1L;
+
     /** Creates a new instance of TreeCategoryImpl */
     public TreeCategoryImpl() {
         super();