"".equals(ret) ? null : ret; 改为 ret != null && ret.length() != 0 ? ret :

null

src/main/java/com/jfinal/core/Controller.java

@@ -167,7 +167,7 @@ public abstract class Controller {
 	public String getPara(String name) {
 		// return request.getParameter(name);
 		String result = request.getParameter(name);
-		return "".equals(result) ? null : result;
+		return result != null && result.length() != 0 ? result : null;
 	}
 	
 	/**