Merge pull request #4301 from conifercone/3.0

完善BaseMapper注释

mybatis-plus-core/src/main/java/com/baomidou/mybatisplus/core/mapper/BaseMapper.java

@@ -184,7 +184,7 @@ public interface BaseMapper<T> extends Mapper<T> {
      * 根据 Wrapper 条件，判断是否存在记录
      *
      * @param queryWrapper 实体对象封装操作类
-     * @return
+     * @return 是否存在记录
      */
     default boolean exists(Wrapper<T> queryWrapper) {
         Long count = this.selectCount(queryWrapper);