[BUG] Release 5.0.5 is bad - multiple issues with code working on past version

Version LiteDB 5.0.5 on dotnet core 3.1 windows and linux

Describe the bug null pointers coming from multi different actions inside LiteDB on code thar was working on version 5.0.4. (was having an issue with records not been found sometimes but i think that relates to bug someelse reported)

Code to Reproduce putting lines from my code so may not be perfect but should give rough idea.

_db = new LiteDatabase( "MappingAndWriteCache.db");
_mappings = _db.GetCollection<MappingRecord>();
_mappings.EnsureIndex("Status", record => record.Status);
_mappings.EnsureIndex("DataSourceFileId", record => record.DataSourceFileId);
_mappings.EnsureIndex("FileId", record => record.FileId);
_mappings.Upsert(new MappingRecord
                {
                    Id = id,
                    FileId = fileId,
                    BlockNbr = blockNbr,
                    DataSourceFileId = null,
                    DataSourceFileBlockOffset = 0,
                    DataSourceFileBlockLength = block.Length,
                    LastModified = DateTime.UtcNow,
                    Status = BlockStatus.New
                });

public enum BlockStatus { New, BatchedForUpload, Uploaded, Empty }

public class MappingRecord
{
    public string Id { get; set; }
    public string FileId { get; set; }
    public uint BlockNbr { get; set; }
    public string DataSourceFileId { get; set; }
    public long DataSourceFileBlockOffset { get; set; }
    public int DataSourceFileBlockLength { get; set; }
    public DateTime LastModified { get; set; }
    public BlockStatus Status { get; set; }
}

Expected behavior Upsert should happen without null pointer below.

Screenshots/Stacktrace

System.NullReferenceException: Object reference not set to an instance of an object.
   at LiteDB.BsonValue.GetHashCode()
   at System.Linq.Set`1.InternalGetHashCode(TElement value)
   at System.Linq.Set`1.Add(TElement value)
   at System.Linq.Enumerable.DistinctIterator`1.MoveNext()
   at LiteDB.Engine.LiteEngine.InsertDocument(Snapshot snapshot, BsonDocument doc, BsonAutoId autoId, IndexService indexer, DataService data)
   at LiteDB.Engine.LiteEngine.<>c__DisplayClass30_0.<Upsert>b__0(TransactionService transaction)
   at LiteDB.Engine.LiteEngine.AutoTransaction[T](Func`2 fn)
   at LiteDB.Engine.LiteEngine.Upsert(String collection, IEnumerable`1 docs, BsonAutoId autoId)
   at LiteDB.LiteCollection`1.Upsert(IEnumerable`1 entities)
   at LiteDB.LiteCollection`1.Upsert(T entity)

Additional context This is the easiest one to isolate but basically all my unit tests over code using litedb is now failing with a lot of null pointers from different calls.

[lbnascimento]

This issue is already fixed in master and its fix will be present in the next incremental release.

[seertenedos]

Great. You should enable a prerelease that always points to the latest master. Then people like myself can test fixes etc and some people may run or test versions before release. I would love to test this fix and the other fix in 5.0.5 to see if it fixes some strangeness i have with records coming back on a find on the first call but not the second right after each other in a transaction for the same record some times.