TypeError: Location.getUsers is not a function

'use strict';

const fs = require('fs');
const path = require('path');
const Sequelize = require('sequelize');
const basename = path.basename(__filename);
const env = process.env.NODE_ENV || 'production';
const config = require(__dirname + '/../config/config.js')[env];
const db = {};

var sequelize = new Sequelize(config.database, config.username, config.password, config);

fs
  .readdirSync(__dirname)
  .filter(file => {
    return (file.indexOf('.') !== 0) && (file !== basename) && (file.slice(-3) === '.js');
  })
  .forEach(file => {
    const model = sequelize['import'](path.join(__dirname, file));
    db[model.name] = model;
  });

Object.keys(db).forEach(modelName => {
  if (db[modelName].associate) {
    db[modelName].associate(db);
  }
});

db.sequelize = sequelize;
db.Sequelize = Sequelize;

module.exports = db;

'use strict';
module.exports = (sequelize, DataTypes) => {
  const Location = sequelize.define('Location', {
    name: {
      allowNull: false,
      type: DataTypes.STRING
    },
  }, {
    sequelize,
    modelName: 'location',
    underscored: true,
  });

  Location.associate = function(models) {
    Location.hasMany(models.User);
  };

  return Location;
};

'use strict';
module.exports = (sequelize, DataTypes) => {
  const User = sequelize.define('User', {
    email: {
      allowNull: false,
      type: DataTypes.STRING
    },
    location_id: {
      type: DataTypes.INTEGER
    },
  }, {
    sequelize,
    modelName: 'user',
    underscored: true
  });
  User.associate = function(models) {
    User.belongsTo(models.Location);
  };
  return User;
};