MailClient Homework

I'm having the following problems and I was wondering if anyone here could help out. The errors are in the following.

Exception in thread "main" java.lang.NullPointerException
at client.Contact.save(Contact.java:35)
at client.Message.save(Message.java:44)
at client.Mailbox.save(Mailbox.java:62)
at client.cmd.Save.run(Save.java:15)
at client.CmdLoop.run(CmdLoop.java:53)
at Main.main(Main.java:41)

Contact.save method. Error appears on "Contact C=nick..."

public void save(AddressBook nick, PrintStream print){
  Contact C=nick.search(NickName);
  if(C!=null)
  {
        print.println(NickName);
  }
  else
  {
       print.println(Email);
  }

Message.save method - Error appear I believe in both to.save and from.save

public void save(AddressBook nick, PrintStream print){
to.save(nick, print);
from.save(nick, print);
print.println(body);
print.println(subject);
print.println(date);}

And lastly, Mailbox.save method - Error appears on "m1.save(nick, myStream)"

public void save(String fileName){
Message m1 = null;
AddressBook nick = null;
File myFile = new File(fileName);
try {
    PrintStream  myStream = new PrintStream(myFile);
    for(int n=0; n < mailbox.size(); n++)
    {
        m1 = mailbox.get(n);
        m1.save(nick, myStream);
    }
} catch (FileNotFoundException e) {System.out.println("Mailbox unable to save to file " + myFile);
    e.printStackTrace();}}

Sorry about formatting, first time using this website.