title: query with FILTER(?document = "uriNode") returns no results
body: <p>I am executing the SPARQL query below with Jena, where <code>uriNode</code> is a <code>String</code> representing a <code>URI</code>, but this query doesn't give me any results.  I've already checked the database and this <code>URI</code> does exist there.  What's the problem? </p>
  
  <pre class="lang-java prettyprint-override"><code>String queryString2 = "PREFIX rdf: &lt;http://www.w3.org/1999/02/22-rdf-syntax-ns#&gt; " +
                      "PREFIX dc: &lt;http://purl.org/dc/elements/1.1/&gt; SELECT ?author WHERE { " +
                      "?document dc:creator ?author." +
                      "FILTER (?document = \"" + uriNode + "\" ). }";
  </code></pre>