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

        long aliasValue = 0;
        UtxoData utxoData = (UtxoData) tx.getCoinData();
        for (UtxoInput input : utxoData.getInputs()) {
            if (input.getFrom() == null) {
                return ValidateResult.getFailedResult(ErrorCode.ORPHAN_TX);
            }
            aliasValue += input.getFrom().getValue();
        }

        if (aliasValue < AccountConstant.ALIAS_NA.add(getLedgerService().getTxFee(TransactionConstant.TX_TYPE_SET_ALIAS)).getValue()) {
            return ValidateResult.getFailedResult("utxo not enough");
        }

        if (tx.getStatus() == TxStatusEnum.CACHED) {
            List<Transaction> txList = getLedgerService().getCacheTxList(TransactionConstant.TX_TYPE_SET_ALIAS);
            if (txList != null && tx.size() > 0) {
                for (Transaction trx : txList) {
                    if(trx.getHash().equals(tx.getHash())) {
                        continue;
                    }
                    Alias a = ((AliasTransaction) trx).getTxData();
                    if (alias.getAddress().equals(a.getAddress())) {
                        return ValidateResult.getFailedResult("Alias has been set up ");
                    }
                    if (alias.getAlias().equals(a.getAlias())) {
                        return ValidateResult.getFailedResult("The alias has been occupied");
                    }
                }
            }
        }

        AliasPo aliasPo = getAliasDataService().get(alias.getAlias());
        if (aliasPo != null) {
            return ValidateResult.getFailedResult("The alias has been occupied");
        }
        return ValidateResult.getSuccessResult();
    } 
                            #location 20 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Override
    public ValidateResult validate(AliasTransaction tx) {
        Alias alias = tx.getTxData();
        if (!Address.validAddress(alias.getAddress())) {
            return ValidateResult.getFailedResult(ErrorCode.ADDRESS_ERROR);
        }
        if (!StringUtils.validAlias(alias.getAlias())) {
            return ValidateResult.getFailedResult(ErrorCode.ALIAS_ERROR);
        }

        long aliasValue = 0;
        UtxoData utxoData = (UtxoData) tx.getCoinData();
        for (UtxoInput input : utxoData.getInputs()) {
            aliasValue += input.getFrom().getValue();
        }

        if (aliasValue < AccountConstant.ALIAS_NA.getValue() + tx.getFee().getValue()) {
            return ValidateResult.getFailedResult(ErrorCode.INVALID_INPUT);
        }

        if (tx.getStatus() == TxStatusEnum.CACHED) {
            List<Transaction> txList = getLedgerService().getCacheTxList(TransactionConstant.TX_TYPE_SET_ALIAS);
            if (txList != null && tx.size() > 0) {
                for (Transaction trx : txList) {
                    if (trx.getHash().equals(tx.getHash())) {
                        continue;
                    }
                    Alias a = ((AliasTransaction) trx).getTxData();
                    if (alias.getAddress().equals(a.getAddress())) {
                        return ValidateResult.getFailedResult(ErrorCode.ACCOUNT_ALREADY_SET_ALIAS);
                    }
                    if (alias.getAlias().equals(a.getAlias())) {
                        return ValidateResult.getFailedResult("The alias has been occupied");
                    }
                }
            }
        }

        AliasPo aliasPo = getAliasDataService().get(alias.getAlias());
        if (aliasPo != null) {
            return ValidateResult.getFailedResult(ErrorCode.ALIAS_EXIST);
        }
        return ValidateResult.getSuccessResult();
    }