title: Check enum null when it is not nullable and do not have any null options
body: <p>This is different from questions like below</p>
  
  <p><a href="https://stackoverflow.com/questions/16554577/how-to-tell-if-an-enum-property-has-been-set-c-sharp">How to tell if an enum property has been set? C#</a></p>
  
  <p>I am working on creating WCF Rest service using existing DataContract classes. I cannot change property datatypes like enum to enum? and also cannot add new option in my enum like undefined, none, or by default set anything since if I do anyone of these changes it will be firm wide impact and many applications depend on it.</p>
  
  <p>Normally people call my WCF REST Service using applications like POSTMAN where they send in json data like below in which Gender is an enum with Male, Female, Transgender, etc. If they do not send it my service throws exception and I want to add validation logic to check whether enum is null or not when QA scall my service using POSTMAN and send JSON data even though it is not nullable and also do not have any None, Null options in my enum? If it is NULL I want to send <code>ArgumentNullException</code> back to callers with nice message. I want to handle this situation gracefully.</p>
  
  <pre><code>public enum Gender 
  {
      Male = 0,
      Female = 1,
      Transgender = 2
  }
  </code></pre>
  
  <p>Below is good</p>
  
  <pre><code>{
        "Name" : "XXX"
        "Gender" : "1"
  }
  </code></pre>
  
  <p>Below throws error</p>
  
  <pre><code>{
        "Name" : "XXX"
        "Gender" : ""
  }
  </code></pre>
  
  <p><strong>SOLUTION:</strong></p>
  
  <p>Thanks to p.s.w.g for pointing in correct direction and I marked his answer below. I am using  Newtonsoft so I did like below</p>
  
  <pre><code>string stringfydata = Newtonsoft.Json.JsonConvert.SerializeObject(requestGender);
  if(string.IsNullOrEmpty(stringfydata))
  {
     throw new ArgumentNullException("Gender value cannot be NULL or Empty.");
  }
  </code></pre>