add test to reproduce #891 bug report

fix bug

meilisearch-core/src/update/documents_addition.rs

@@ -201,12 +201,14 @@ pub fn apply_addition<'a, 'b>(
             };
 
             let old_document = Option::<HashMap<String, Value>>::deserialize(&mut deserializer)?;
+        println!("old document: {:#?}", old_document);
             if let Some(old_document) = old_document {
                 for (key, value) in old_document {
                     document.entry(key).or_insert(value);
                 }
             }
         }
+        println!("new document: {:#?}", document);
         documents_additions.insert(internal_docid, document);
     }
 

meilisearch-core/src/update/helpers.rs

@@ -20,6 +20,7 @@ pub fn index_value<A>(
 ) -> Option<usize>
 where A: AsRef<[u8]>,
 {
+    println!("indexing value: {}", value);
     match value {
         Value::Null => None,
         Value::Bool(boolean) => {

meilisearch-core/src/update/settings_update.rs

@@ -70,9 +70,11 @@ pub fn apply_settings_update(
 
     match settings.searchable_attributes.clone() {
         UpdateState::Update(v) => {
+            println!("updating indexed attributes");
             if v.iter().any(|e| e == "*") || v.is_empty() {
                 schema.set_all_fields_as_indexed();
             } else {
+                println!("updating indexed");
                 schema.update_indexed(v)?;
             }
             must_reindex = true;