title: Unknown property in Angular object
body: <p>While sending object to the backend <strong>UnrecognizedPropertyException</strong> appears. I have checked object on both frontend and backend side and it looks the same.</p>
  <p>However when I am checking this object at frontend console I can see that it has additional property that is not defined nowhere in the project (I've tried to search it on IntelliJ ctrl + shift + f).</p>
  <p>This property was in the object some time ago so it is possible that somehow it is cashed?
  I've tried to clear cache / invalidate cache in IntelliJ / npm clean-install etc.</p>
  <p>How can I check from where this property appears in object ?</p>
  <p><em>@JsonIgnoreProperties</em> is not an option in my case...</p>
  <p>Frontend object (Angular 8 + Typescript 2.6.2):</p>
  <pre><code>export class ItemEto extends AbstractEto {
      item1: number;
      item2: number;
  }
  
  export class AbstractEto {
      id: number;
      modificationCounter: number;
  }
  </code></pre>
  <p>Backend object (Java 8):</p>
  <pre><code>public class ItemEto extends AbstractEto {
      private long item1;
      private long item2;
  }
  
  public class AbstractEto {
      private long id;
      private long modificationCounter;
  }
  </code></pre>
  <p>Object on console (JSON):</p>
  <pre><code>{
      &quot;ItemEto&quot;: {
          &quot;item1&quot;: 1,
          &quot;item2&quot;: 2,
          &quot;otherUnknownProperty&quot;: {
              &quot;item3&quot;: null;
          },
      }
  }
  </code></pre>