fix: IsDefined + IsOptional combination return error 500 instead of 400 (bad request)

[luanpersini]

Description

I have a DTO class with a param that is an object. Ive set it to defined and optional. Somehow, if i remove the optional, the validation goes ok (returns 400), if i keep the isOptional, it returns error 500. Its not validating as expected and the application cannot deal with the null value.

Minimal code-snippet showcasing the problem

 @IsDefined()
 @IsNotEmptyObject()
 @IsObject()
 @ValidateNested()
 @ApiProperty({
    example: AccountDto,
    description: 'Account information.',
  })
  @Type(() => AccountDto)
  @IsOptional()
  account!: AccountDto;

 //request
 
{
account: null
}

Expected behavior

Should return error 400 bad request, since its undefined.

Actual behavior

It throws internal server error (isnt returning the error 400)