title: What's the suitable HTTP error for non requested required data
body: <p>In my case there is no parameters required. In other words, the application does not expect any data via post, get or put. However, in the implementation a stored list of items in session variable should be defined first i.e. something like shopping cart items, the user collect items, and then go to the action below, otherwise, it should throw an HTTP error. Checkout the example below:</p>
  <pre><code>public function actionCreate(){
    if(count(Yii::$app-&gt;session-&gt;get('versesList',[])) &gt; 0){
      // Do the logic
    }
    else{
      throw new \yii\web\BadRequestHttpException(Yii::t('app', 'You must collect some verses first!')); 
    }
  }
  </code></pre>
  <p>I don't know exactly, if the 400 bad request is the proper error code or not. I have tried reading <a href="https://en.wikipedia.org/wiki/List_of_HTTP_status_codes#5xx_Server_errors" rel="nofollow noreferrer">List of HTTP status codes</a> on the Wikipedia but I have gotten confused among some of the other HTTP errors such as: <code>406 Not Acceptable</code>, <code>412 Precondition Failed</code>,<code>422 Unprocessable Entity</code></p>