♻ #12633

src/main/java/org/b3log/solo/repository/ArticleRepository.java

@@ -262,6 +262,10 @@ public class ArticleRepository extends AbstractRepository {
      */
     public JSONObject getPreviousArticle(final String articleId) throws RepositoryException {
         final JSONObject currentArticle = get(articleId);
+        if (null == currentArticle) {
+            return null;
+        }
+
         final long currentArticleCreated = currentArticle.optLong(Article.ARTICLE_CREATED);
 
         final Query query = new Query().
@@ -309,6 +313,10 @@ public class ArticleRepository extends AbstractRepository {
      */
     public JSONObject getNextArticle(final String articleId) throws RepositoryException {
         final JSONObject currentArticle = get(articleId);
+        if (null == currentArticle) {
+            return null;
+        }
+
         final long currentArticleCreated = currentArticle.optLong(Article.ARTICLE_CREATED);
 
         final Query query = new Query().

src/main/java/org/b3log/solo/service/ArticleMgmtService.java

@@ -727,12 +727,19 @@ public class ArticleMgmtService {
             if (tagIdList.isEmpty()) { // Removes all if un-specified
                 relationId = tagArticleRelation.getString(Keys.OBJECT_ID);
                 tagArticleRepository.remove(relationId);
+
             } else {
                 if (tagIdList.contains(tagArticleRelation.getString(Tag.TAG + "_" + Keys.OBJECT_ID))) {
                     relationId = tagArticleRelation.getString(Keys.OBJECT_ID);
                     tagArticleRepository.remove(relationId);
                 }
             }
+
+            final String tagId = tagArticleRelation.optString(Tag.TAG + "_" + Keys.OBJECT_ID);
+            final int articleCount = tagArticleRepository.getArticleCount(tagId);
+            if (1 > articleCount) {
+                tagRepository.remove(tagId);
+            }
         }
     }