Cannot $set length field

[jidambo]

When try to set length field to the document I have N null fields. Tried findOneAndUpdate and update methods.

const setLength = async () => {
  const _id = {your_id};
  const length = 20; // Note: only for number, string works as expected
  
  await db.collection.findOneAndUpdate({_id}, {$set: {length: length}});
}

setLength()

expected result:

db.collection.findOne({_id}) 

{
    _id: {your_id},
    length: 20
}

sad reality:

db.collection.findOne({_id}) 

{
    _id: {your_id},
    "0" : null,
    "1" : null,
    "2" : null,
    "3" : null,
    "4" : null,
    "5" : null,
    "6" : null,
    "7" : null,
    "8" : null,
    "9" : null,
    "10" : null,
    "11" : null,
    "12" : null,
    "13" : null,
    "14" : null,
    "15" : null,
    "16" : null,
    "17" : null,
    "18" : null,
    "19" : null
}

[jidambo]

Sorry to bother you. We've added a custom middleware that modifies $set body on update.
Be careful with custom middlewares!