title: FieldValue arrayUnion and Cloud FireStore with Flutter
body: <p>I have cloud fire store object like this</p>
  
  <pre><code>"TestCollection" : ["Test1","Test"]
  </code></pre>
  
  <p>Now I want to update this array with FieldValue.arrayUnion
  because if element is same then i don't want to do anything but if it is not then I would like to add element</p>
  
  <pre><code>docRef.updateData({"TestCollection":FieldValue.arrayUnion(["test"])})
  </code></pre>
  
  <p>but this statement gives the error like object can not have nested array</p>
  
  <p>Can anyone please help or provide same kind of example to have look for syntax ?</p>