title: bool.fromEnvironment always return false
body: <p>Here's a code:</p>
  
  <pre><code>const bool a = const bool.fromEnvironment("true");
  print(a); // false
  </code></pre>
  
  <p>Yes, default value is false by default. What should I do that <code>a</code> will be true, without using default value? And what is the string parameter? is it a key maybe?</p>