You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: simple_id_tracker.rs
    path of file: ./repos/qdrant/lib/segment/src/id_tracker
    
    the code of the file until where you have to start completion: use std::collections::BTreeMap;
use std::sync::Arc;

use bincode;
use bitvec::prelude::{BitSlice, BitVec};
use common::types::PointOffsetType;
use parking_lot::RwLock;
use rocksdb
    
    fn external_id(&self, internal_id: PointOffsetType) -> Option<PointIdType> {
        if let Some(deleted) = self.deleted.get(internal_id as usize) {
            if !deleted {
                return self.internal_to_external.get(internal_id as usize).copied();
            }
        }
        None
    }