diff between existing and plausable hotfix

hotfix.diff

diff --git a/kinto/core/storage/postgresql/migrations/migration_019_hotfix.sql b/kinto/core/storage/postgresql/migrations/migration_019_hotfix.sql
index 1795b55a..bab9234d 100644
--- a/kinto/core/storage/postgresql/migrations/migration_019_hotfix.sql
+++ b/kinto/core/storage/postgresql/migrations/migration_019_hotfix.sql
@@ -5,29 +5,36 @@ RETURNS trigger AS $$
 DECLARE
     previous TIMESTAMP;
     current TIMESTAMP;
+    is_bucket BOOLEAN;
 BEGIN
+    current := clock_timestamp();
+
     previous := NULL;
-    WITH existing_timestamps AS (
-      -- Timestamp of latest record.
-      (
-        SELECT last_modified
-        FROM records
-        WHERE parent_id = NEW.parent_id
-          AND collection_id = NEW.collection_id
-        ORDER BY last_modified DESC
-        LIMIT 1
-      )
-      -- Timestamp when collection was empty.
-      UNION
-      (
-        SELECT last_modified
-        FROM timestamps
-        WHERE parent_id = NEW.parent_id
-          AND collection_id = NEW.collection_id
-      )
-    )
-    SELECT MAX(last_modified) INTO previous
-      FROM existing_timestamps;
+
+    is_bucket := NEW.parent_id = '' AND NEW.collection_id = 'bucket';
+    IF NOT is_bucket THEN
+        WITH existing_timestamps AS (
+          -- Timestamp of latest record.
+          (
+            SELECT last_modified
+            FROM records
+            WHERE parent_id = NEW.parent_id
+              AND collection_id = NEW.collection_id
+            ORDER BY last_modified DESC
+            LIMIT 1
+          )
+          -- Timestamp when collection was empty.
+          UNION
+          (
+            SELECT last_modified
+            FROM timestamps
+            WHERE parent_id = NEW.parent_id
+              AND collection_id = NEW.collection_id
+          )
+        )
+        SELECT MAX(last_modified) INTO previous
+          FROM existing_timestamps;
+    END IF;
 
     --
     -- This bumps the current timestamp to 1 msec in the future if the previous
@@ -38,7 +45,6 @@ BEGIN
     -- an error (operation is cancelled).
     -- See https://github.com/mozilla-services/cliquet/issues/25
     --
-    current := clock_timestamp();
     IF previous IS NOT NULL AND previous >= current THEN
         current := previous + INTERVAL '1 milliseconds';
     END IF;