diff --git a/milli/src/update/facet/incremental.rs b/milli/src/update/facet/incremental.rs
index 584870a7a..798e0fe3d 100644
--- a/milli/src/update/facet/incremental.rs
+++ b/milli/src/update/facet/incremental.rs
@@ -18,6 +18,32 @@ use crate::update::index_documents::valid_lmdb_key;
 use crate::update::MergeFn;
 use crate::{CboRoaringBitmapCodec, Index, Result};
 
+/// Enum used as a return value for the facet incremental indexing.
+///
+/// - `ModificationResult::InPlace` means that modifying the `facet_value` into the `level` did not have
+/// an effect on the number of keys in that level. Therefore, it did not increase the number of children
+/// of the parent node.
+///
+/// - `ModificationResult::Insert` means that modifying the `facet_value` into the `level` resulted
+/// in the addition of a new key in that level, and that therefore the number of children
+/// of the parent node should be incremented.
+///
+/// - `ModificationResult::Remove` means that modifying the `facet_value` into the `level` resulted in a change in the
+/// number of keys in the level. For example, removing a document id from the facet value `3` could
+/// cause it to have no corresponding document in level 0 anymore, and therefore the key was deleted
+/// entirely. In that case, `ModificationResult::Remove` is returned. The parent of the deleted key must
+/// then adjust its group size. If its group size falls to 0, then it will need to be deleted as well.
+///
+/// - `ModificationResult::Reduce/Expand` means that modifying the `facet_value` into the `level` resulted in a change in the
+/// bounds of the keys of the level. For example, removing a document id from the facet value
+/// `3` might have caused the facet value `3` to have no corresponding document in level 0. Therefore,
+/// in level 1, the key with the left bound `3` had to be changed to the next facet value (e.g. 4).
+/// In that case `ModificationResult::Reduce` is returned. The parent of the reduced key may need to adjust
+/// its left bound as well.
+///
+/// - `ModificationResult::Nothing` means that modifying the `facet_value` didn't have any impact into the `level`.
+/// This case is reachable when a document id is removed from a sub-level node but is still present in another one.
+/// For example, removing `2` from a document containing `2` and `3`, the document id will removed form the `level 0` but should remain in the group node [1..4] in `level 1`.
 enum ModificationResult {
     InPlace,
     Expand,
@@ -315,6 +341,9 @@ impl FacetsUpdateIncrementalInner {
         Ok(ModificationResult::Insert)
     }
 
+    /// Remove the docids still present in the related sub-level nodes from the del_docids.
+    ///
+    /// This process is needed to avoid removing docids from a group node where the docid is present in several sub-nodes.
     fn trim_del_docids<'a>(
         &self,
         txn: &mut RwTxn,
@@ -352,30 +381,6 @@ impl FacetsUpdateIncrementalInner {
     /// ## Return
     /// Returns the effect of modifying the facet value to the database on the given `level`.
     ///
-    /// - `ModificationResult::InPlace` means that modifying the `facet_value` into the `level` did not have
-    /// an effect on the number of keys in that level. Therefore, it did not increase the number of children
-    /// of the parent node.
-    ///
-    /// - `ModificationResult::Insert` means that modifying the `facet_value` into the `level` resulted
-    /// in the addition of a new key in that level, and that therefore the number of children
-    /// of the parent node should be incremented.
-    ///
-    /// - `ModificationResult::Remove` means that modifying the `facet_value` into the `level` resulted in a change in the
-    /// number of keys in the level. For example, removing a document id from the facet value `3` could
-    /// cause it to have no corresponding document in level 0 anymore, and therefore the key was deleted
-    /// entirely. In that case, `ModificationResult::Remove` is returned. The parent of the deleted key must
-    /// then adjust its group size. If its group size falls to 0, then it will need to be deleted as well.
-    ///
-    /// - `ModificationResult::Reduce/Expand` means that modifying the `facet_value` into the `level` resulted in a change in the
-    /// bounds of the keys of the level. For example, removing a document id from the facet value
-    /// `3` might have caused the facet value `3` to have no corresponding document in level 0. Therefore,
-    /// in level 1, the key with the left bound `3` had to be changed to the next facet value (e.g. 4).
-    /// In that case `ModificationResult::Reduce` is returned. The parent of the reduced key may need to adjust
-    /// its left bound as well.
-    ///
-    /// - `ModificationResult::Nothing` means that modifying the `facet_value` didn't have any impact into the `level`.
-    /// This case is reachable when a document id is removed from a sub-level node but is still present in another one.
-    /// For example, removing `2` from a document containing `2` and `3`, the document id will removed form the `level 0` but should remain in the group node [1..4] in `level 1`.
     fn modify_in_level(
         &self,
         txn: &mut RwTxn,
@@ -465,7 +470,7 @@ impl FacetsUpdateIncrementalInner {
 
         if updated_value.size < self.max_group_size {
             // If there are docids to delete, trim them avoiding unexpected removal.
-            let del_docids = del_docids
+            if let Some(del_docids) = del_docids
                 .map(|ids| {
                     self.trim_del_docids(
                         txn,
@@ -477,8 +482,8 @@ impl FacetsUpdateIncrementalInner {
                     )
                 })
                 .transpose()?
-                .filter(|ids| !ids.is_empty());
-            if let Some(del_docids) = del_docids {
+                .filter(|ids| !ids.is_empty())
+            {
                 updated_value.bitmap -= &*del_docids;
                 insertion_value_was_modified = true;
             }