Java Please help. So many Errors I don't know what I'm doing wrong but apparently its a lot

You'll Just have to run it yourself everything goes wrong when I hit calculate.

This is all the errors I get:

Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: empty String
    at sun.misc.FloatingDecimal.readJavaFormatString(Unknown Source)
    at sun.misc.FloatingDecimal.parseDouble(Unknown Source)
    at java.lang.Double.parseDouble(Unknown Source)
    at java.lang.Double.valueOf(Unknown Source)
    at school.TravelExpenses$CalcButtonListener.actionPerformed(TravelExpenses.java:139)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$500(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)

Code:

package school;

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.JOptionPane;

/**
 * The TravelExpense class creates the GUI for the Travel Expenses application.
 */

public class TravelExpenses extends JFrame {
    // The following variables will reference the
    // custom panel objects
    private JPanel travelInfoPanel; // TravelInfo panel
    private JPanel buttonPanel; // Buttons panel

    // Labels for the Travel Information fields.
    private JLabel DaysLabel;
    private JLabel AirfareLabel;
    private JLabel CarLabel;
    private JLabel MilesLabel;
    private JLabel ParkingLabel;
    private JLabel CabLabel;
    private JLabel RegistrLabel;
    private JLabel LodgingLabel;

    // Text Fields for Travel Information entry
    private JTextField DaysTextField;
    private JTextField AirfareTextField;
    private JTextField CarTextField;
    private JTextField MilesTextField;
    private JTextField ParkingTextField;
    private JTextField CabTextField;
    private JTextField RegistrTextField;
    private JTextField LodgingTextField;

    private JButton calcButton;

    private double mealsReimbursed = 37.00;
    private double parkingReimbursed = 10.00;
    private double taxiChargesReimbursed = 20.00;
    private double lodgingChargesReimbursed = 95.00;
    private double perMileReimbursed = 0.27;
    public TravelExpenses() {
        super("Travel Expenses");

        setLocationRelativeTo(null);

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        setLayout(new BorderLayout());

        buildTravelInfoPanel();
        buildButtonPanel();

        add(travelInfoPanel, BorderLayout.CENTER);
        add(buttonPanel, BorderLayout.SOUTH);

        pack();
        setVisible(true);
    }


    private void buildTravelInfoPanel() {
        DaysLabel = new JLabel("Number of days on trip: ");
        AirfareLabel = new JLabel("Amount of airfare: ");
        CarLabel = new JLabel("Amount of car rental: ");
        MilesLabel = new JLabel("Miles driven: ");
        ParkingLabel = new JLabel("Parking Fees: ");
        CabLabel = new JLabel("Taxi fees: ");
        RegistrLabel = new JLabel("Conference registration: ");
        LodgingLabel = new JLabel("Lodging charges per night: ");

        DaysTextField = new JTextField(3);
        AirfareTextField = new JTextField(8);
        CarTextField = new JTextField(8);
        MilesTextField = new JTextField(4);
        ParkingTextField = new JTextField(6);
        CabTextField = new JTextField(6);
        RegistrTextField = new JTextField(8);
        LodgingTextField = new JTextField(6);

        travelInfoPanel = new JPanel();

        travelInfoPanel.setLayout(new GridLayout(10, 2));

        travelInfoPanel.add(DaysLabel);
        travelInfoPanel.add(DaysTextField);
        travelInfoPanel.add(AirfareLabel);
        travelInfoPanel.add(AirfareTextField);
        travelInfoPanel.add(CarLabel);
        travelInfoPanel.add(CarTextField);
        travelInfoPanel.add(MilesLabel);
        travelInfoPanel.add(MilesTextField);
        travelInfoPanel.add(ParkingLabel);
        travelInfoPanel.add(ParkingTextField);
        travelInfoPanel.add(CabLabel);
        travelInfoPanel.add(CabTextField);
        travelInfoPanel.add(RegistrLabel);
        travelInfoPanel.add(RegistrTextField);
        travelInfoPanel.add(LodgingLabel);
        travelInfoPanel.add(LodgingTextField);

        // Add an empty border around the panel for spacing.
        travelInfoPanel.setBorder(BorderFactory
                .createEmptyBorder(10, 10, 1, 10));
    }

    private void buildButtonPanel() {
        // Create the calcButton.
        calcButton = new JButton("Calculate");

        calcButton.addActionListener(new CalcButtonListener());

        buttonPanel = new JPanel();

        buttonPanel.setLayout(new BorderLayout(5, 5));

        // Add the two buttons to the buttonPanel.
        buttonPanel.add(calcButton, BorderLayout.CENTER);

        buttonPanel.setBorder(BorderFactory.createEmptyBorder(1, 10, 10, 10));
    }

    private class CalcButtonListener implements ActionListener {

        String days = DaysTextField.getText();
        String air = AirfareTextField.getText();
        String carRental = CarTextField.getText();
        String miles = MilesTextField.getText();
        String parking =ParkingTextField.getText();
        String taxi = CabTextField.getText();
        String Registr = RegistrTextField.getText();
        String lodging = LodgingTextField.getText();

        public void actionPerformed(ActionEvent e) {
            // Declare variables for calculated items
            double actualExpenses=Double.valueOf(air) + Double.valueOf(carRental) + Double.valueOf(parking) + Double.valueOf(taxi) + Double.valueOf(Registr) + Double.valueOf(lodging) + (Double.valueOf(miles)*.27);
            double allowableExpenses=(mealsReimbursed+parkingReimbursed+taxiChargesReimbursed+lodgingChargesReimbursed)*Integer.valueOf(days)+perMileReimbursed;
            double excessAmount=actualExpenses-allowableExpenses;
            String savedMoney="Owed";
            if(excessAmount<0){
                savedMoney="Saved";
                excessAmount*=-1;
            }
            JOptionPane.showMessageDialog(null, "Total Expenses: "+actualExpenses+"\nAllowable Expenses: "+allowableExpenses+"\n"+"Money "+savedMoney+": "+excessAmount);
        }
    }

    public static void main(String[] args) {
        new TravelExpenses();
    }
}