Getting an error when deploying to heroku "TypeError: Parameter 'url' must be a string, not undefined"

I am trying to deploy my app to heroku but it's throwing this error that I listed in the title. I'll attach my server.js file and db.js file to see if someone can spot what is crashing the deploy. I think I am getting the error from my db.js file:

db.js

var Sequelize = require('sequelize');
var env = process.env.NODE_ENV || 'development';
var sequelize;

if (env === 'production') {
    sequelize = new Sequelize(process.env.DATABASE_URL, {
        dialect: 'postgres'
    }); // This if statement should execute if the app is run on Heroku
} else {
    sequelize = new Sequelize(undefined, undefined, undefined, {
        'dialect': 'sqlite',
        'storage': __dirname + '/data/practice-todo-api.sqlite'
    });
}



var db = {};

db.todo = sequelize.import(__dirname + '/models/todo.js');
db.user = sequelize.import(__dirname + '/models/user.js');
db.token = sequelize.import(__dirname + '/models/token.js');
db.sequelize = sequelize;
db.Sequelize = Sequelize;

db.todo.belongsTo(db.user);
db.user.hasMany(db.todo);

module.exports = db;