allow all models to be created with no data

[dwhieb]

Often a model will need to be instantiated with no data. Though in many cases this violates the DLx spec (for example, the Language model requires a name field), it's necessary to allow this for data entry purposes.

Tests

  it(`new Language()`, function() {
    expect(() => new Language()).not.toThrow();
    expect(() => new Language({})).not.toThrow();
  });