title: Breeze error: Illegal construction - use 'or' to combine checks
body: <p>I met this Breeze error </p>
  
  <blockquote>
    <p>[Illegal construction - use 'or' to combine checks]  </p>
  </blockquote>
  
  <p>on Chrome when loading the edit page of an entity. When I refresh the page, the error message no longer appears. This error happens randomly, irregularly on my site. I could not reproduce it using a specified scenario, just met it by random.</p>
  
  <p>I see this error message inside Breeze code</p>
  
  <pre><code>if (curContext.prevContext === null) {
      curContext.prevContext = context;
      // just update the prevContext but don't change the curContext.
      return that;
  } else if (context.prevContext === null) {
      context.prevContext = that._context;
  } else {
      throw new Error("Illegal construction - use 'or' to combine checks");
  }
  </code></pre>
  
  <p>Could you please tell me: based on above block of code, in which cases this error is thrown?</p>
  
  <p>Thanks a lot.</p>