Validate strings with many zeros

Question

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

however cnpj can come with 0 or 000 or 0000000 or 00, which would give in the same...

I am currently doing the validation below however, I was asked to change the validation != 0 for something more "elegant", someone has some idea of 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