Refs #3163, #3227, make sure no exception thrown in tracker when no 'ua'...

Refs #3163, #3227, make sure no exception thrown in tracker when no 'ua' parameter & no HTTP_USER_AGENT. (fix for bug in [6737]).


git-svn-id: http://dev.piwik.org/svn/trunk@6887 59fd770c-687e-43c8-a1e3-f5a4ff64c105

core/Tracker/Visit.php

@@ -654,7 +654,8 @@ class Piwik_Tracker_Visit implements Piwik_Tracker_Visit_Interface
 	 */
 	protected function getUserAgent()
 	{
-	    return Piwik_Common::getRequestVar('ua', @$_SERVER['HTTP_USER_AGENT'], 'string', $this->request);
+		$default = @$_SERVER['HTTP_USER_AGENT'];
+		return Piwik_Common::getRequestVar('ua', is_null($default) ? false : $default, 'string', $this->request);
 	}
 	
 	/**