title: Ignore property when null using the new Net Core 3.0 Json
body: <p>When using JSON.Net in ASP.Net Core 2.2 I was able to ignore a property when its value was null when serializing to JSON:</p>
  
  <pre><code>[JsonProperty(NullValueHandling = NullValueHandling.Ignore)]
  public DateTime? Created { get; set; }
  </code></pre>
  
  <p>But when using the new ASP.Net Core 3.0 built in JSON (System.Text.Json) I can’t find an equivalent attribute to ignore a property if its value is null.</p>
  
  <p>I could only find JsonIgnore.</p>
  
  <p>Am I missing something?</p>