Validate strings with many zeros

I have to perform a validation on a trigger in sql server the rule is: if cnpj is! = 0 and does not exist in another continue record;

But cnpj can come with 0 or 000 or 0000000 or 00, which would be the same ...

I am currently doing the validation below but they asked me to change the validation! = 0 to something more "elegant", does anyone have any idea how I can do this?

 IF 0 != CONVERT(bigint,(SELECT CGC_CPF FROM inserted)) 
  BEGIN 
    if EXISTS(SELECT * FROM CADASTRO_CLI_FOR A 
                  LEFT JOIN FILIAIS B ON A.COD_CLIFOR=B.COD_FILIAL 
                        WHERE A.CGC_CPF=@CNPJ
                        AND B.INDICA_ARMAZEM =0)
  begin
      select @errno  = 30002,
             @errmsg = 'Impossível Incluir #FORNECEDORES #porque CNPJ #ja existe.'
      goto error
    end
  end

  return