let jackson create the list

src/main/java/de/thm/arsnova/controller/SessionController.java

@@ -272,15 +272,14 @@ public class SessionController extends PaginationController {
 	@ApiOperation(value = "export sessions", nickname = "exportSession")
 	@RequestMapping(value = "/export", method = RequestMethod.GET)
 	public List<ImportExportSession> exportSession(
-			@ApiParam(value = "comma seperated list of sessionkeys", required = true) @RequestParam(value = "sessionkeys", defaultValue = "") final String sessionkeys,
+			@ApiParam(value = "sessionkey", required = true) @RequestParam(value = "sessionkey", defaultValue = "") final List<String> sessionkey,
 			@ApiParam(value = "wether statistics shall be exported", required = true) @RequestParam(value = "withAnswerStatistics", defaultValue = "false") final Boolean withAnswerStatistics,
 			@ApiParam(value = "wether interposed questions shall be exported", required = true) @RequestParam(value = "withFeedbackQuestions", defaultValue = "false") final Boolean withFeedbackQuestions,
 			@ApiParam(value = "http servlet response", required = true) final HttpServletResponse response
 		) {
 		List<ImportExportSession> sessions = new ArrayList<ImportExportSession>();
 		ImportExportSession temp;
-		String[] splittedKeys = sessionkeys.split(",");
-		for (String key : splittedKeys) {
+		for (String key : sessionkey) {
 			sessionService.setActive(key, false);
 			temp = sessionService.exportSession(key, withAnswerStatistics, withFeedbackQuestions);
 			if (temp != null) {