Deserializing object to array

I have a field with mixed type (object or array of object). Now I am trying to deserialize this field into array of object with this

class AssociationSerializer : SerializerBase<Association[]>
{
    public override Association[] Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
    {
        var type = context.Reader.GetCurrentBsonType();

        switch (type)
        {
            case BsonType.Array:
                var arraySerializer = new ArraySerializer<Association>();
                return arraySerializer.Deserialize(context, new BsonDeserializationArgs());

            case BsonType.Document:
                var bsonDocument = context.Reader.ToBsonDocument();
                var association= BsonSerializer.Deserialize<Association>(bsonDocument);
                return new[] { association };

            default:
                throw new NotSupportedException();
        }
    }
}

But I am getting this error

System.InvalidOperationException: ReadBsonType can only be called when State is Type, not when State is Value.
at MongoDB.Bson.IO.BsonReader.ThrowInvalidState(String methodName, BsonReaderState[] validStates)
at MongoDB.Bson.IO.BsonBinaryReader.ReadBsonType()
at MongoDB.Bson.Serialization.BsonClassMapSerializer1.DeserializeClass(BsonDeserializationContext context) at MongoDB.Bson.Serialization.BsonClassMapSerializer1.Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
at MongoDB.Bson.Serialization.IBsonSerializerExtensions.Deserialize[TValue](IBsonSerializer`1 serializer, BsonDeserializationContext context)

Not sure what I am doing wrong.

public class Association
{
    public string Id { get; set; }
    public int Type { get; set; }
}

JSON:

{   
    "association" : [
        {
            "_id" : "b8e0a770-951b-5e85-84a6-8ca8cd0998e0",
            "type" : 0
        }
    ]
}   
    
{
    "association" : {
        "_id" : "08dc1cb0-0f88-4dcf-70db-ff3b8c000003"
    }
}

A simplest approach I see:

 public class AssociationSerializer : SerializerBase<Association[]>
 {
     public override Association[] Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
     {
         var type = context.Reader.GetCurrentBsonType();

         switch (type)
         {
             case BsonType.Array:
                 var arraySerializer = new ArraySerializer<Association>();
                 return arraySerializer.Deserialize(context, new BsonDeserializationArgs());

             case BsonType.Document:
                 var value = BsonSerializer.Deserialize<Association>(context.Reader);
                 return new[] { value };

             default:
                 throw new NotSupportedException();
         }
     }
 }