Removed unnecessary [NotNull] attributes

In a previous commit, I introduced the `[ValidatedNotNull]` attribute to assure Code Analysis that the base methods in `TopicRepositoryBase` were performing parameter validation and, thus, could be assured that those parameters would not be `null`.

That was a necessary and useful addition. When I did that, however, I also added `[NotNull]`. There are cases where this makes sense. But it doesn't make sense here, since the value of the parameters is already marked as not nullable.

In fact, this causes newer versions of Roslyn's static flow analysis to identify this as a mismatch between these versions of the methods and the methods that `override` them in e.g. `SqlTopicRepository`.

This seems like a false positive to me, and I could even see that being a nuissance in other scenarios, but as it's the attribute isn't even needed here, we'll evaluate that issue if and when we come across a scenario where it really is a problem.

Author: JeremyCaney

OnTopic/Repositories/TopicRepositoryBase.cs

@@ -234,7 +234,7 @@ protected virtual ContentTypeDescriptorCollection SetContentTypeDescriptors(Cont
     | METHOD: ROLLBACK
     \-------------------------------------------------------------------------------------------------------------------------*/
     /// <inheritdoc />
-    public virtual void Rollback([ValidatedNotNull, NotNull]Topic topic, DateTime version) {
+    public virtual void Rollback([ValidatedNotNull]Topic topic, DateTime version) {
 
       /*------------------------------------------------------------------------------------------------------------------------
       | Validate parameters
@@ -300,7 +300,7 @@ public virtual void Rollback([ValidatedNotNull, NotNull]Topic topic, DateTime ve
     | METHOD: SAVE
     \-------------------------------------------------------------------------------------------------------------------------*/
     /// <inheritdoc />
-    public virtual int Save([ValidatedNotNull, NotNull]Topic topic, bool isRecursive = false, bool isDraft = false) {
+    public virtual int Save([ValidatedNotNull]Topic topic, bool isRecursive = false, bool isDraft = false) {
 
       /*------------------------------------------------------------------------------------------------------------------------
       | Validate parameters
@@ -387,7 +387,7 @@ topic is ContentTypeDescriptor descriptor &&
     | METHOD: MOVE
     \-------------------------------------------------------------------------------------------------------------------------*/
     /// <inheritdoc />
-    public virtual void Move([ValidatedNotNull, NotNull]Topic topic, [ValidatedNotNull, NotNull]Topic target) {
+    public virtual void Move([ValidatedNotNull]Topic topic, [ValidatedNotNull]Topic target) {
 
       /*------------------------------------------------------------------------------------------------------------------------
       | Validate parameters
@@ -409,7 +409,7 @@ public virtual void Move([ValidatedNotNull, NotNull]Topic topic, [ValidatedNotNu
     /// <param name="target">A topic object under which to move the source topic.</param>
     /// <param name="sibling">A topic object representing a sibling adjacent to which the topic should be moved.</param>
     /// <returns>Boolean value representing whether the operation completed successfully.</returns>
-    public virtual void Move([ValidatedNotNull, NotNull]Topic topic, [ValidatedNotNull, NotNull]Topic target, Topic? sibling) {
+    public virtual void Move([ValidatedNotNull]Topic topic, [ValidatedNotNull]Topic target, Topic? sibling) {
 
       /*------------------------------------------------------------------------------------------------------------------------
       | Validate parameters
@@ -455,7 +455,7 @@ public virtual void Move([ValidatedNotNull, NotNull]Topic topic, [ValidatedNotNu
     | METHOD: DELETE
     \-------------------------------------------------------------------------------------------------------------------------*/
     /// <inheritdoc />
-    public virtual void Delete([ValidatedNotNull, NotNull]Topic topic, bool isRecursive) {
+    public virtual void Delete([ValidatedNotNull]Topic topic, bool isRecursive) {
 
       /*------------------------------------------------------------------------------------------------------------------------
       | Validate parameters