title: ConstraintSet clone crash
body: <p>I am trying to clone the ConstraintSet like:</p>
  
  <pre><code>        ConstraintLayout cl = findViewById(R.id.mainActivityParentCl);
          ConstraintSet constraintSet = new ConstraintSet();
          constraintSet.clone(cl);
  </code></pre>
  
  <p>It crashes on clone(cl), </p>
  
  <pre><code>Caused by: java.lang.RuntimeException: All children of ConstraintLayout must have ids to use ConstraintSet
  </code></pre>
  
  <p>It doesnt crash when using </p>
  
  <pre><code>implementation 'com.android.support.constraint:constraint-layout:1.0.2'
  </code></pre>
  
  <p>It crashes on 1.1.3: </p>
  
  <pre><code>implementation 'com.android.support.constraint:constraint-layout:1.1.3'
  </code></pre>
  
  <p>Solution?</p>