问Java TableRowSorter中的NullPointerException

EN

chemicalTable.setAutoCreateRowSorter(true);
TableRowSorter<TableModel> sorter1 
      = new TableRowSorter<TableModel>(chemicalTable.getModel());
chemicalTable.setRowSorter(sorter1);

DefaultTableModel dm = (DefaultTableModel) chemicalTable.getModel();

str = searchChemicalText.getText();

        try {
            String url = "jdbc:mysql://localhost/chemical inventory";
            Class.forName("com.mysql.jdbc.Driver").newInstance();
            conn = DriverManager.getConnection(url, "root", "");


        } catch (Exception e) {
            JOptionPane.showMessageDialog(this, "Error Occurred.", "Error", JOptionPane.ERROR_MESSAGE);
        }

        int ctr = 0;


        while (ctr < chemicalTable.getRowCount()) {
            chemicalTable.getModel().setValueAt(null, ctr, 0);
            chemicalTable.getModel().setValueAt(null, ctr, 1);
            chemicalTable.getModel().setValueAt(null, ctr, 2);
            ctr++;

        }

        int count = 0;

        try {
            Statement stmt = conn.createStatement();
            String query = "Select * FROM chemicallist where name_of_reagent like '%" + str + "%'";
            ResultSet rs = stmt.executeQuery(query);

            if (rs.next()) {
                rs = stmt.executeQuery(query);

                while (rs.next()) {
                    String qty = null, qtyunit = null, chemstate = null, reagentName = null;

                    reagentName = rs.getString("name_of_reagent");
                    qty = rs.getString("quantity");
                    qtyunit = rs.getString("quantity_unit");
                    chemstate = rs.getString("state");
                    chemicalTable.getModel().setValueAt(reagentName, count, 0);
                    chemicalTable.getModel().setValueAt(qty + " " + qtyunit, count, 1);
                    chemicalTable.getModel().setValueAt(chemstate, count, 2);



                    if (count + 1 > chemicalTable.getRowCount() - 1) {
                        dm.setRowCount(chemicalTable.getRowCount() + 1);
                        dm.fireTableRowsInserted(0, 5);


                    }
                    count++;


                }
            }
        } catch (Exception e) {
            JOptionPane.showMessageDialog(this, "Error Occurred.", "Error", JOptionPane.ERROR_MESSAGE);


        }