feat: ignore 'None' abstract

custom_pgvector.py

@@ -354,7 +354,9 @@ class CustomPGVector(VectorStore):
                     left join keyword on article_keyword.keyword_id = keyword.id
                     left join article_author ON article_author.article_id = a.id
                     left join author on author.id = article_author.author_id  
-                    where abstract_en != ''
+                    where
+                        abstract_en != '' and
+                        abstract_en != 'None'
                     GROUP BY a.id
                     ORDER BY distance
                     LIMIT {k};