Eigenschaft '2' von null kann nicht gelesen werden

pragma solidity ^0.4.23;

import'./ID.sol';
import'./Whitelisted.sol';

contract IDFactory is Ownable {

    Whitelisted whitelist;

    event IDCreated(uint id, address idContractAddress);

    mapping (uint => address) public ids;

    modifier idExists(uint id) {
      require(ids[id]);
      _;
     }
      constructor() public {
        owner = msg.sender;
        whitelist = new Whitelisted(owner);
        whitelist.addToWhitelist(owner);
    }
}

Hallo, ich versuche, einen Soliditätsvertrag mit Trüffel zu erstellen. Der Vertrag heißt IDFactory.sol. Wenn ich die Truffle-Kompilierung ausführe, erhalte ich diesen Fehler:

MacBook-Pro-de-Alicia-2:a alicialombarte$ truffle compile
TypeError: Error parsing /Users/alicialombarte/notary-contract/a/contracts/IDFactory.sol: Cannot read property '2' of null
    at /usr/local/lib/node_modules/truffle/build/webpack:/~/truffle-core/~/truffle-compile/parser.js:171:1
    at Array.map (<anonymous>)
    at Object.parseImports (/usr/local/lib/node_modules/truffle/build/webpack:/~/truffle-core/~/truffle-compile/parser.js:167:6)
    at /usr/local/lib/node_modules/truffle/build/webpack:/~/truffle-core/~/truffle-compile/profiler.js:302:1
    at /usr/local/lib/node_modules/truffle/build/webpack:/~/truffle-resolver/index.js:79:1
    at /usr/local/lib/node_modules/truffle/build/webpack:/~/truffle-resolver/~/async/internal/onlyOnce.js:12:1
    at next (/usr/local/lib/node_modules/truffle/build/webpack:/~/truffle-resolver/~/async/whilst.js:68:1)
    at /usr/local/lib/node_modules/truffle/build/webpack:/~/truffle-resolver/index.js:64:1
    at /usr/local/lib/node_modules/truffle/build/webpack:/~/truffle-resolver/fs.js:85:1
    at /usr/local/lib/node_modules/truffle/build/webpack:/~/truffle-resolver/~/async/internal/once.js:12:1

Ich habe keine 2 in meinem Vertrag.

Vielen Dank!

Hier sind die anderen 2 Verträge:

pragma solidity ^0.4.23;

import'./Whitelisted.sol';

contract ID{

    uint id;
    Whitelisted whitelist;
    mapping (string => MessageData) public messages;

    event MessageSaved(string messageHash);

    constructor(uint _id, address _whitelist) public {
        owner = msg.sender;
        id = _id;
        whitelist = Whitelisted(_whitelist);
    }

    struct MessageData {
        string messageSender;
        uint64 timestamp;
    }
}

pragma solidity ^0.4.23;

import 'Ownable.sol';

contract Whitelisted is Ownable {

    constructor(_owner) public {
        owner = _owner;
    }

    mapping(address => bool) internal whitelistedAddresses;

    function isWhitelisted(address addr) internal view returns (bool) {
        return whitelistedAddresses[addr];
    }

    function addToWhitelist(address addr) public onlyOwner {
        require(!isWhitelisted(addr));
        whitelistedAddresses[addr] = true;
    }

    function removeFromWhitelist(address addr) public onlyOwner {
        require(isWhitelisted(addr));
        whitelistedAddresses[addr] = false;
    }

    modifier onlyWhitelisted {
        require(isWhitelisted(msg.sender));
        _;
    }
}