#vulnerable code 
                                @Override
    public ValidateResult validate(AliasTransaction tx) {
        Alias alias = tx.getTxData();
        if (StringUtils.isBlank(alias.getAddress()) || new Address(alias.getAddress()).getHash160().length > 25) {
            return ValidateResult.getFailedResult("The address format error");
        }
        if (!StringUtils.validAlias(alias.getAlias())) {
            return ValidateResult.getFailedResult("The alias is between 3 to 20 characters");
        }

        AliasPo aliasPo = aliasDataService.get(alias.getAlias());
        if (aliasPo != null) {
            return ValidateResult.getFailedResult("The alias has been occupied");
        }
        return ValidateResult.getSuccessResult();
    } 
                            #location 4 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Override
    public ValidateResult validate(AliasTransaction tx) {
        Alias alias = tx.getTxData();
        if (StringUtils.isBlank(alias.getAddress()) || new Address(alias.getAddress()).getHash().length !=23 ) {
            return ValidateResult.getFailedResult("The address format error");
        }
        if (!StringUtils.validAlias(alias.getAlias())) {
            return ValidateResult.getFailedResult("The alias is between 3 to 20 characters");
        }

        AliasPo aliasPo = aliasDataService.get(alias.getAlias());
        if (aliasPo != null) {
            return ValidateResult.getFailedResult("The alias has been occupied");
        }
        return ValidateResult.getSuccessResult();
    }