Description

The new command previously allowed the --lang flag to be passed without a value (e.g., ember new my-app --lang), resulting in the project being created with an empty language string.

This PR adds a check to ensure that if --lang is present, it must have a value. If not, it rejects with a SilentError.

Reproduction

1. Run ember new my-app --lang
2. Observe that the app is created successfully (unexpected behavior).

Solution

Added a validation check in lib/commands/new.js and a corresponding unit test in tests/unit/commands/new-test.js.