[2.0] Added exception if query builder is missing from or select when trying to get dql string

lib/Doctrine/ORM/QueryBuilder.php

@@ -21,7 +21,8 @@
 
 namespace Doctrine\ORM;
 
-use Doctrine\ORM\Query\Expr;
+use Doctrine\ORM\Query\Expr,
+    Doctrine\Common\DoctrineException;
 
 /**
  * This class is responsible for building DQL query strings via an object oriented
@@ -191,6 +192,10 @@ class QueryBuilder
             return $this->_dql;
         }
 
+        if ( ! $this->_dqlParts['select'] || ! $this->_dqlParts['from']) {
+            throw DoctrineException::incompleteQueryBuilder();
+        }
+
         $dql = '';
 
         switch ($this->_type) {