How do I refresh a JList with updated SQLite database information whenever items are added/deleted?

I'm trying to make a program right now that will edit the Employee's info database using SQLite. On the left side of my frame I have a JList and in the menu I can add employee's, save/edit them, and delete them.

I have it set up to call this method when the frame is made:

try {
  tempName = null;
  query = "Select FirstName,LastName FROM EmployeeInfo";
  pst4 = connection.prepareStatement(query);
  rs4 = pst4.executeQuery();

  while(rs4.next()){
    tempName = rs4.getString("FirstName") + " " + rs4.getString("LastName");
    listNames.add(tempName);
   }
    list.setListData(listNames);

    pst4.close();
    rs4.close();

   }catch (Exception e1) {
    JOptionPane.showMessageDialog(null, "Problem loading Employee List." + e1); 
    e1.printStackTrace();
    }

and then after a Save, Delete, or Add I call this method to "refresh" it: (almost identical to the first method)

listNames.removeAllElements();
try {
  tempName = null;
  query = "Select FirstName,LastName FROM EmployeeInfo";
  pst4 = connection.prepareStatement(query);
  rs4 = pst4.executeQuery();

  while(rs4.next()){
    tempName = rs4.getString("FirstName") + " " + rs4.getString("LastName");
    listNames.add(tempName);
   }
    list.setListData(listNames);

    pst4.close();
    rs4.close();

   }catch (Exception e1) {
    JOptionPane.showMessageDialog(null, "Problem loading Employee List." + e1); 
    e1.printStackTrace();
    }

listNames is a Vector<String>

My delete and save buttons work find on updating the JList with this method, but for my add one it's having issues. I have it set up to open up a new JDialog Frame with a WindowListener on it. Whenever the window closes it calls the same exact method I've been using above but I get a NullPointException. It seems to work fine even with the error but I feel like there's a much better way to handle this.

Any help is appreciated.