NameConflictTreeWalk: Mark repo param @Nullable

This is passed directly to the super constructor, where it is also
@Nullable. Marking it here saves the reader a jump.

Change-Id: Icc8db2f2dc6aae6e591aa4f09a3c283336a5424c

org.eclipse.jgit/src/org/eclipse/jgit/treewalk/NameConflictTreeWalk.java

@@ -45,6 +45,7 @@ package org.eclipse.jgit.treewalk;
 
 import java.io.IOException;
 
+import org.eclipse.jgit.annotations.Nullable;
 import org.eclipse.jgit.dircache.DirCacheBuilder;
 import org.eclipse.jgit.errors.CorruptObjectException;
 import org.eclipse.jgit.lib.FileMode;
@@ -110,7 +111,7 @@ public class NameConflictTreeWalk extends TreeWalk {
 	 *            the reader the walker will obtain tree data from.
 	 * @since 4.3
 	 */
-	public NameConflictTreeWalk(Repository repo, final ObjectReader or) {
+	public NameConflictTreeWalk(@Nullable Repository repo, final ObjectReader or) {
 		super(repo, or);
 	}