run:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at mylibrary.implemen.PenerbitImpl.getAll(PenerbitImpl.java:34)
at mylibrary.view.AddBukuPanel.isiPenerbitBox(AddBukuPanel.java:34)
at mylibrary.view.AddBukuPanel.<init>(AddBukuPanel.java:44)
at mylibrary.view.HomePanel.initComponents(HomePanel.java:48)
at mylibrary.view.HomePanel.<init>(HomePanel.java:23)
at mylibrary.view.MainFrame.initComponents(MainFrame.java:60)
at mylibrary.view.MainFrame.<init>(MainFrame.java:36)
at mylibrary.view.MainFrame.getMainFrame(MainFrame.java:234)
at mylibrary.MyLibrary$1.run(MyLibrary.java:48)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:705)
at java.awt.EventQueue.access$000(EventQueue.java:101)
at java.awt.EventQueue$3.run(EventQueue.java:666)
at java.awt.EventQueue$3.run(EventQueue.java:664)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:675)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:211)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:128)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:117)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:113)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:90)
BUILD SUCCESSFUL (total time: 1 second)

public class PenerbitImpl implements PenerbitlInface{

private Connection conn;

@Override
public List<penerbit> getAll() throws SQLException {
List<penerbit> p = new ArrayList<>();
try {
conn = Koneksi.getConn();
PreparedStatement stmt = conn.prepareStatement("SELECT * FROM penerbit"); (line 34)
ResultSet rs = stmt.executeQuery();
while (rs.next()) {
penerbit pen = new penerbit();
pen.setId(rs.getInt("idPenerbit"));
pen.setNama(rs.getString("nama"));
pen.setAlamat(rs.getString("alamat"));
pen.setEmail(rs.getString("email"));
pen.setWebsite(rs.getString("website"));
pen.setKota(rs.getString("kota"));
pen.setTelepon(rs.getString("telepon"));
p.add(pen);
}
} catch (SQLException | ClassNotFoundException ex) {
Logger.getLogger(AddBukuPanel.class.getName()).log(Level.SEVERE, null, ex);
}

return p;
}

}