title: Codable All Key Decode as Optional But Not Optional
body: <p>Codable is easy to use and don't code samething to much</p>
  
  <p>but when i use add new variable to the Codable after update the app</p>
  
  <p>JSONDecoder throws KeyNotFoundError</p>
  
  <p>if i declear variable as Optional, It will not throw KeyNotFoundError</p>
  
  <p>but every thing is Optional is bad to use</p>
  
  <p>how can i change the decode strategy to "if Key not exits, just ignore the variable" and every variable is not Optional and don't write echo variable for decodeIfPresent() ?</p>
  
  <pre><code>class Student: Coadable {
      var name:String = "TheDefaultIWent" ;
      ...ManyVarsInThisClass...
  }
  </code></pre>