[BUG] Adding an immutable record to LiteDB gives an NRE

Version: LiteDB 5.0.3, Windows, NetCore3.1

Describe the bug Adding an immutable record to LiteDB gives an NRE, although the document is actually inserted.

Code to Reproduce

open LiteDB

type Customer = {
    Id : int
    Name : string
    Phones : string array
    IsActive : bool
}

let db = new LiteDatabase("MyData.db")
let col = db.GetCollection "customers"

let customer =
    { Id = 0
      Name = "John Doe"
      Phones = [| "8000-0000"; "9000-0000" |]
      IsActive = true }

// Insert new customer document (Id will be auto-incremented)
col.Insert customer |> ignore

Expected behavior The record should be inserted without an exception.

System.NullReferenceException: Object reference not set to an instance of an object. at LiteDB.LiteCollection1.Insert(T entity)`

Additional context You can work around this by marking the record type with [<CLIMutable>]. However, this is non-idomatic from an F# perspective.

[lbnascimento]

@humhei This happens because ObjectId implements IComparable<ObjectId>, but not IComparable (an oversight, I believe). Try using Guid as Id, it should work.

[Zaid-Ajaj]

There is already an opened issue about updating LiteDB.FSharp to latest LiteDB version. I won’t be able to work on it any time soon due to other prioritized projects. Feel free to send PRs for the issue in subject, I will be happy to review them