title: SPARQL replace empty attributes with others
body: <p>I made a SPARQL query using the official DBpedia endpoint.</p>
  
  <p>I'll take it for example for the main Question:</p>
  
  <pre><code>SELECT  ?museum ?EnglishAbstract   ?RussianAbstract 
  WHERE { 
  
  ?museum dbpedia-owl:abstract ?EnglishAbstract. 
  ?museum a dbpedia-owl:Museum.
  filter(lang(?EnglishAbstract)='en')
  
  optional{
      ?museum dbpedia-owl:abstract ?RussianAbstract.
      ?museum a dbpedia-owl:Museum.
  filter(lang(?RussianAbstract)='ru')
  }}
  GROUP BY ?museum
  </code></pre>
  
  <p>With this query (that works good), I find for every row (<code>museum</code>) a bunch of Abstract in 2 languages: English and Russian.
  The Russian abstracts are present only if available because I use "OPTIONAL".
  Obviously I get a lot of empty attributes.</p>
  
  <p>I would replace the blank attribute with the English abstract (always present).</p>
  
  <p>Reading the W3C SPARQL page, I found that there is a particular testing value that is true when a variable is set: Bound</p>
  
  <p>I would like to write something like this:</p>
  
  <pre><code>If Bound (?RussianAbstract), "?RussianAbstract", "?EnglishAbstract"
  </code></pre>
  
  <p>-->  if <code>RussianAbstract</code> is present, hold it; else, put the <code>EnglishAbstract</code> instead of it.</p>
  
  <p>Does anyone know how can I make it work?</p>