add validate condition

src/entities/rank-record.entity.ts

 import { Column, Entity, Index, SelectQueryBuilder } from 'typeorm';
 import { IdBase } from './bases/IdBase.entity';
 import { StringColumn } from './decorators/base';
-import { IsDate } from 'class-validator';
+import { IsDate, ValidateIf } from 'class-validator';
 import { ApiProperty } from '@nestjs/swagger';
 import { Session } from 'koishi';
 import { applyQueryProperty, applyQueryPropertySearch } from './utility/query';
@@ -23,6 +23,7 @@ export class RankRecord extends IdBase {
   rankDate: Date;
 
   @Index()
+  @ValidateIf((v) => v?.length)
   @StringColumn(6, 'Rank content', undefined, true)
   rankName: string;