#vulnerable code 
                              @Test
  public void testConvertFlatToProgressiveAgg() throws VerdictDBValueException {
    SelectQuery aggQuery = SelectQuery.create(
        ColumnOp.count(),
        new BaseTable("myschema", "mytable", "t"));
    AggExecutionNode aggnode = AggExecutionNode.create(aggQuery, "myschema");
    AggExecutionNodeBlock block = new AggExecutionNodeBlock(aggnode);
    ScrambleMeta scrambleMeta = generateTestScrambleMeta();
    QueryExecutionNode converted = block.convertToProgressiveAgg(scrambleMeta);
    converted.print();
  } 
                            #location 10 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                              @Test
  public void testConvertFlatToProgressiveAgg() throws VerdictDBValueException {
    SelectQuery aggQuery = SelectQuery.create(
        new AliasedColumn(ColumnOp.count(), "agg"),
        new BaseTable(newSchema, newTable, "t"));
    AggExecutionNode aggnode = AggExecutionNode.create(aggQuery, newSchema);
    AggExecutionNodeBlock block = new AggExecutionNodeBlock(aggnode);
    QueryExecutionNode converted = block.convertToProgressiveAgg(newSchema, scrambleMeta);
    converted.print();
    converted.execute(new JdbcConnection(conn, new H2Syntax()));
  }