title: Update document field with solrj
body: <p>I want to edit document filed in solr,for example edit the author name,so i use the following code in solrj:</p>
  
  <pre><code>params.set("literal.author","anaconda")
  </code></pre>
  
  <p>but the author multivalued="true" in schema and because of that "anaconde" is not replace with it's previous name and add to the end of the author name,also if i ommit the multivalued field or set it to false the bad request exception happen in re-indexing file with new author field,how can i solve this problem and delete or modify the previous document field in solrj?
  or does it any config i miss in schema?
  thanks</p>