INVALID_FORM is thrown when the form declared in signin method is not found

[gregorylegarec]

When using:

function authenticate(username, password) {
  return signin({
    debug: true,
    url: 'https://www.mywebsite.fr/login/',
    formSelector: '.login_wrapper form',
    formData: { email: username, password },
    validate: () => true
  })
}

When the form is not found, an INVALID_FORM error is thrown and it could make the developer think that the selector used is bad.