LoopBack: findOne() returns non-empty result if value of filter criteria is undefined

car.json

{
  "name": "Car",
  "plural": "Cars",
  "base": "PersistedModel",
  "properties": {
    "number": {
      "type": "string",
      "required": true
    }
  },
  "validations": [],
  "relations": {},
  "acls": [],
  "methods": []
}

cars_test.js

var app = require('../server/server');
var request = require('supertest');
var assert = require('assert');

describe('Create and query car', function() {
  var newCar = { number: "1234" };
  var Car = app.models.Car;

  before(function() {
    Car.create(newCar);
  });

  describe('REST API', function() {

    it('should find by existing number', function (done) {

      request(app)
        .get('/api/cars/findOne?filter[where][number]=1234')
        .set('Content-Type', 'application/json')
        .expect(200)
        .end(function (err, res) {
          if (err) {
            return done(err);
          }

          assert.equal(res.body.number, newCar.number);
          done();
        });
    });

    it('should find any if query number is not specified', function(done) {
      request(app)
        .get('/api/cars/findOne')
        .set('Content-Type', 'application/json')
        .expect(200)
        .end(function (err, res) {
          if (err) {
            return done(err);
          }
          assert.equal(res.body.number, newCar.number);
          done();
        });
    });

    it('should not find if query number is empty', function(done) {
      request(app)
        .get('/api/cars/findOne?filter[where][number]=')
        .set('Content-Type', 'application/json')
        .expect(404)
        .end(function (err, res) {
          if (err) {
            return done(err);
          }
          done();
        });
    });
  });

  describe('NODE API', function() {

    it('should find by existing number', function (done) {
      Car.findOne({ where: { number: "1234" }}, function(err, car) {
        if (err) {
          return done(err);
        } else {
          assert.equal(car.number, newCar.number);
          done();
        }
      });
    });

    it('should find if query not specified', function(done) {
      Car.findOne(function(err, car) {
        if (err) {
          return done(err);
        } else {
          assert.equal(car.number, newCar.number);
          done();
        }
      });
    });

    it('should not find if query number is empty string', function(done) {
      Car.findOne({ where: { number: "" }}, function(err, car) {
        if (err) {
          return done(err);
        } else {
          assert.ok(car == null);
          done();
        }
      });
    });

    it('should not find if query number is "undefined"', function(done) {
      Car.findOne({ where: { number: undefined }}, function(err, car) {
        if (err) {
          return done(err);
        } else {
          assert.ok(car == null, "Found car by incomplete query");
          done();
        }
      });
    });
  });

});

output

$ mocha tests/*


  Create and query car
    REST API
      ✓ should find by existing number 
      ✓ should find any if query number is not specified 
      ✓ should not find if query number is empty 
    NODE API
      ✓ should find by existing number 
      ✓ should find if query not specified 
      ✓ should not find if query number is empty string 
      1) should not find if query number is "undefined"


  6 passing (41ms)
  1 failing

  1) Create and query car NODE API should not find if query number is "undefined":
     Uncaught AssertionError: Found car by incomplete query