Why this java.lang.NullPointerException error?

Question

I'm a rookie java programmer and I'm trying to build a system where I add items a user inputs to a jtable but each attempt to add items leads to a java.lang.NullPointerException error when it gets to the quantity to be added. I don't seem to know what is going on. Quantity was declared as an object in jtable properties. Help, please. I received the Exception at warehouses.addItem(item);

This is the code to add item

 private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    String itemName = itemnamTxtfld.getText(), serialNum = itemSerialNotxtfld.getText(), seller = sellerTxtfld.getText(),
            expDate = expDateFmtFld.getText(); int quantity = 0;


    if (itemnamTxtfld.getText().isEmpty()) {
        JOptionPane.showMessageDialog(this, "Input Item Name", "Input Error", JOptionPane.WARNING_MESSAGE);
        return;
    } else if (!itemSerialNotxtfld.getText().matches("(\\d{3}-?){2}\\d{4}")) {
        JOptionPane.showMessageDialog(this, "Input Item Serial Number", "Input Error", JOptionPane.WARNING_MESSAGE);
        return;
    } else if (sellerTxtfld.getText().isEmpty()) {
        JOptionPane.showMessageDialog(this, "Input seller", "Input Error", JOptionPane.WARNING_MESSAGE);
        return;
    } //^\d{2}-?\d{2}-?\d{4}$   //^((19|2[0-9])[0-9]{2})-(0[1-9]|1[012])-(0[1-9]|[12][0-9]|3[01])$
    else if (!quantityTxtfld.getText().isEmpty()) {
        try {
            quantity = Integer.parseInt(quantityTxtfld.getText());
        } catch (NumberFormatException e) {
            JOptionPane.showMessageDialog(this, "Quantity must be a Number", "Quantity Error", JOptionPane.WARNING_MESSAGE);
            return;
        }
    }
    if (quantityTxtfld.getText().isEmpty()) {
        JOptionPane.showMessageDialog(this, "Input quantity", "Input Error", JOptionPane.WARNING_MESSAGE);
    } else if (expDateFmtFld.getText().isEmpty()) {
        JOptionPane.showMessageDialog(this, "Input Date", "Input Error", JOptionPane.WARNING_MESSAGE);
        return;
    }
    if (!expDateFmtFld.getText().matches("^(0[1-9]|[12][0-9]|3[01])-(0[1-9]|1[012])-((20|2[0-9])[0-9]{2})$")) {
        JOptionPane.showMessageDialog(this, "Input Date", "Input Error", JOptionPane.WARNING_MESSAGE);
        return;
    } else {
        itemAccount Itemaccount = null;
        if(typeComboBox.getSelectedItem().toString() == "Alcoholic"){
            Itemaccount = new Alcoholic(quantity);
        }else if(typeComboBox.getSelectedItem().toString() == "Non Alcoholic"){
            Itemaccount = new NonAlcoholic(quantity);
        }else if(typeComboBox.getSelectedItem().toString() == "Beverage"){
            Itemaccount = new Beverage(quantity);
        }else if(typeComboBox.getSelectedItem().toString() == "Biscuit"){
            Itemaccount = new Biscuit(quantity);
        }else if(typeComboBox.getSelectedItem().toString() == "Food Stuff"){
            Itemaccount = new FoodStuff(quantity);
        }else{
        int confirm = JOptionPane.showConfirmDialog(this, "Do you want to add item?", "Add Item", JOptionPane.YES_NO_OPTION);
        if (confirm == JOptionPane.YES_OPTION){
        item = new Item(itemName, serialNum, seller, expDate, Itemaccount);
        warehouses.addItem(item);
        this.dispose();}
        else{
            this.dispose();
        }
    }
} }                                       

code to add item to table

  public void addItemToTable(Item item){

    model.addRow(new Object[]{});
    reloadItemRowData(model.getRowCount() - 1, item);

to add item to arraylist

  ArrayList<Item> goods = new ArrayList<Item>();

void addItem(Item item){
    if(itemtExists(item.getItemAccount().getItemID())){
        item.getItemAccount().setItemID(findValidItemNumber());
    }
    goods.add(item);
}

item class

class Item {

private WarehouseApp warehouse;


private final String itemName;
private final String serialNum;
private final String seller;
private final String expDate;
private itemAccount Itemaccount;




Item(String itemName, String serialNum, String seller, String expDate, itemAccount Itemaccount){
    this.itemName = itemName;
    this.serialNum = serialNum;
    this.seller = seller;
    this.expDate = expDate;
    this.Itemaccount = Itemaccount;

}    
  /**
 * @return the itemName
 */


public String getItemName() {
    return itemName;
}

/**
 * @return the serialNum
 */
public String getSerialNum() {
    return serialNum;
}

/**
 * @return the seller
 */
public String getSeller() {
    return seller;
}

/**
 * @return the expDate
 */
public String getExpDate() {
    return expDate;
}

itemAccount getItemAccount() {
    return Itemaccount;    
}}

get and set quantity

public abstract class itemAccount {

private int quantity = 0;
private int itemID;
private static int NumberOfItems = 1000;

itemAccount(){
    itemID = getNextItemID();
}
public int getQuantity() {
    return quantity;
}

public void setQuantity(int quantity) {
    this.quantity = quantity;
}