Simplify StringUtils

mybatis-plus/src/main/java/com/baomidou/mybatisplus/toolkit/StringUtils.java

@@ -66,7 +66,7 @@ public class StringUtils {
      * @return 转换好的字符串
      */
     public static String camelToUnderline(String param) {
-        if (StringUtils.isEmpty(param)) {
+        if (isEmpty(param)) {
             return "";
         }
         int len = param.length();