title: check if value exists inside Json response flutter
body: <p>I made a <code>Json</code> post request and got a response that looks like this:</p>
  
  <pre><code>[{id: 13, mentor_id: 5, mentee_id: 184, status: null, session_count: 0, current_job: null, email: null, phone_call: null, video_call: null, face_to_face: null, created_at: 2020-02-20 20:37:50, updated_at: 2020-02-20 20:37:50}, {id: 14, mentor_id: 8, mentee_id: 184, status: null, session_count: 0, current_job: null, email: null, phone_call: null, video_call: null, face_to_face: null, created_at: 2020-02-21 22:39:31, updated_at: 2020-02-21 22:39:31}]
  </code></pre>
  
  <p>Now, I want to check if the <code>id</code> key is equal to a certain number so I could set a button's state. For example:</p>
  
  <pre><code>if(id contains 5){
  ....
  }
  </code></pre>
  
  <p>How do I achieve that in flutter?</p>