output: #fixed code
                               @Override
  	public String visitQuery_specification(VerdictSQLParser.Query_specificationContext ctx) {
  		StringBuilder sql = new StringBuilder(2000);
  		
  		// this statement computes the mean value
  		AnalyticSelectStatementRewriter meanRewriter = new AnalyticSelectStatementRewriter(vc, queryString);
  		meanRewriter.setDepth(depth+1);
  		meanRewriter.setIndentLevel(defaultIndent + 6);
  		String mainSql = meanRewriter.visit(ctx);
  		cumulativeReplacedTableSources.putAll(meanRewriter.getCumulativeSampleTables());
  		
  		// this statement computes the standard deviation
  		BootstrapSelectStatementRewriter varianceRewriter = new BootstrapSelectStatementRewriter(vc, queryString);
  		varianceRewriter.setDepth(depth+1);
  		varianceRewriter.setIndentLevel(defaultIndent + 6);
  		String subSql = varianceRewriter.varianceComputationStatement(ctx);
  		
  		String leftAlias = genAlias();
  		String rightAlias = genAlias();
  		
  		// we combine those two statements using join.
  		List<Pair<String, String>> thisColumnName2Aliases = new ArrayList<Pair<String, String>>();
  		
  		List<Pair<String, String>> leftColName2Aliases = meanRewriter.getColName2Aliases();
  //		List<Boolean> leftAggColIndicator = meanRewriter.getAggregateColumnIndicator();
  		
  		List<Pair<String, String>> rightColName2Aliases = varianceRewriter.getColName2Aliases();
  //		List<Boolean> rightAggColIndicator = varianceRewriter.getAggregateColumnIndicator();
  		
  		sql.append(String.format("%sSELECT", indentString));
  		int leftSelectElemIndex = 0;
  		int totalSelectElemIndex = 0;
  		for (Pair<String, String> colName2Alias : leftColName2Aliases) {
  			leftSelectElemIndex++;
  			if (leftSelectElemIndex == 1) sql.append(" ");
  			else sql.append(", ");
  			
  			if (meanRewriter.isAggregateColumn(leftSelectElemIndex)) {
  				// mean
  				totalSelectElemIndex++;
  				String alias = genAlias();
  				sql.append(String.format("%s.%s AS %s", leftAlias, colName2Alias.getRight(), alias));
  				thisColumnName2Aliases.add(Pair.of(colName2Alias.getLeft(), alias));
  				
  				// error (standard deviation * 1.96 (for 95% confidence interval))
  				totalSelectElemIndex++;
  				alias = genAlias();
  				String matchingAliasName = null;
  				for (Pair<String, String> r : rightColName2Aliases) {
  					if (colName2Alias.getLeft().equals(r.getLeft())) {
  						matchingAliasName = r.getRight();
  					}
  				}
  				sql.append(String.format(", %s.%s AS %s", rightAlias, matchingAliasName, alias));
  				thisColumnName2Aliases.add(Pair.of(colName2Alias.getLeft(), alias));
  				
  				meanColIndex2ErrColIndex.put(totalSelectElemIndex-1, totalSelectElemIndex);
  			} else {
  				totalSelectElemIndex++;
  				sql.append(String.format("%s.%s AS %s", leftAlias, colName2Alias.getRight(), colName2Alias.getRight()));
  				thisColumnName2Aliases.add(Pair.of(colName2Alias.getLeft(), colName2Alias.getRight()));
  			}
  		}
  		colName2Aliases = thisColumnName2Aliases;
  		
  		sql.append(String.format("\n%sFROM (\n", indentString));
  		sql.append(mainSql);
  		sql.append(String.format("\n%s     ) AS %s", indentString, leftAlias));
  		sql.append(" LEFT JOIN (\n");
  		sql.append(subSql);
  		sql.append(String.format("%s) AS %s", indentString, rightAlias));
  		sql.append(String.format(" ON %s.l_shipmode = %s.l_shipmode", leftAlias, rightAlias));
  		
  		return sql.toString();
  	}
input: #vulnerable code 
                               @Override
  	public String visitQuery_specification(VerdictSQLParser.Query_specificationContext ctx) {
  		List<Pair<String, String>> subqueryColName2Aliases = null;
  		BootstrapSelectStatementRewriter singleRewriter = null;
  		
  		StringBuilder unionedFrom = new StringBuilder(2000);
  		int trialNum = vc.getConf().getInt("bootstrap_trial_num");
  		for (int i = 0; i < trialNum; i++) {
  			singleRewriter = new BootstrapSelectStatementRewriter(vc, queryString);
  			singleRewriter.setIndentLevel(2);
  			singleRewriter.setDepth(1);
  			String singleTrialQuery = singleRewriter.visitQuery_specificationForSingleTrial(ctx);
  			if (i == 0) {
  				subqueryColName2Aliases = singleRewriter.getColName2Aliases();
  			}
  			if (i > 0) unionedFrom.append("\n  UNION\n");
  			unionedFrom.append(singleTrialQuery);
  		}
  		
  		StringBuilder sql = new StringBuilder(2000);
  		sql.append("SELECT");
  		int selectElemIndex = 0;
  		for (Pair<String, String> e : subqueryColName2Aliases) {
  			selectElemIndex++;
  			sql.append((selectElemIndex > 1)? ", " : " ");
  			if (singleRewriter.isAggregateColumn(selectElemIndex)) {
  				String alias = genAlias();
  				sql.append(String.format("AVG(%s) AS %s",
  						e.getRight(), alias));
  				colName2Aliases.add(Pair.of(e.getLeft(), alias));
  			} else {
  				if (e.getLeft().equals(e.getRight())) sql.append(e.getLeft());
  				else sql.append(String.format("%s AS %s", e.getLeft(), e.getRight()));
  				colName2Aliases.add(Pair.of(e.getLeft(), e.getRight()));
  			}
  		}
  		sql.append("\nFROM (\n");
  		sql.append(unionedFrom.toString());
  		sql.append("\n) AS t");
  		sql.append("\nGROUP BY");
  		for (int colIndex = 1; colIndex <= subqueryColName2Aliases.size(); colIndex++) {
  			if (!singleRewriter.isAggregateColumn(colIndex)) {
  				if (colIndex > 1) {
  					sql.append(String.format(", %s", subqueryColName2Aliases.get(colIndex-1).getRight()));
  				} else {
  					sql.append(String.format(" %s", subqueryColName2Aliases.get(colIndex-1).getRight()));
  				}
  			}
  		}
  		
  		return sql.toString();
  	} 
                              #location 23 
                              #vulnerability type NULL_DEREFERENCE