title: How to query SOLR for empty fields?
body: <p>I have a large solr index, and I have noticed some fields are not updated correctly (the index is dynamic).</p>
  
  <p>This has resulted in some fields having an empty "id" field.</p>
  
  <p>I have tried these queries, but they didn't work:</p>
  
  <pre><code> id:''
   id:NULL
   id:null
   id:""
   id:
   id:['' TO *]
  </code></pre>
  
  <p>Is there a way to query empty fields?</p>
  
  <p>Thanks</p>