Merge #3577

3577: Avoid fetching an LMDB value with an empty string r=ManyTheFish a=Kerollmops

# Pull Request

## Related issue
Fixes #3574 

## What does this PR do?
This PR fixes a bug where an empty key fetches an entry in the database. LMDB throws an error if an empty or too-long key is used to fetch an entry. This empty string seems to have been generated by the Charabia tokenizer.

Co-authored-by: Clément Renault <clement@meilisearch.com>

meilisearch/tests/search/mod.rs

@@ -192,6 +192,31 @@ async fn test_kanji_language_detection() {
         .await;
 }
 
+#[cfg(feature = "default")]
+#[actix_rt::test]
+async fn test_thai_language() {
+    let server = Server::new().await;
+    let index = server.index("test");
+
+    // We don't need documents, the issue is on the query side only.
+    let documents = json!([
+        { "id": 0, "title": "สบู่สมุนไพรดอกดาวเรือง 100 กรัม จำนวน 6 ก้อน" },
+        { "id": 1, "title": "สบู่สมุนไพรชาเขียว 100 กรัม จำนวน 6 ก้อน" },
+        { "id": 2, "title": "สบู่สมุนไพรฝางแดงผสมว่านหางจรเข้ 100 กรัม จำนวน 6 ก้อน" }
+    ]);
+    index.add_documents(documents, None).await;
+    index.wait_task(0).await;
+
+    index.update_settings(json!({"rankingRules": ["exactness"]})).await;
+    index.wait_task(1).await;
+
+    index
+        .search(json!({"q": "สบู"}), |response, code| {
+            assert_eq!(code, 200, "{}", response);
+        })
+        .await;
+}
+
 #[actix_rt::test]
 async fn search_multiple_params() {
     let server = Server::new().await;

milli/src/search/query_tree.rs

@@ -792,6 +792,10 @@ where
 
     let mut peekable = query.peekable();
     while let Some(token) = peekable.next() {
+        if token.lemma().is_empty() {
+            continue;
+        }
+
         // early return if word limit is exceeded
         if primitive_query.len() >= parts_limit {
             return primitive_query;