Fixing - Sparql bug 

The `graph` param passed to `SparqlQueryExecuter ` would be empty all times so any request filtering using sparql queries would return exceptions like : https://gist.github.com/dav009/485b6c2281247669ff89

Here is a sample I query I ran which generate errors in the current master branch, and seems to be fixed with this patch: https://gist.github.com/dav009/3a8eb39dabbc9b4903a8