Automatic use of toString() in println

Question

Hi.
A novice here preparing for the Java 2 Programmer exam. Came across a question in one of the books and I'm left slightly confused about something which I can't get answered. Here goes...
class ToString
     public static void main( String[] args ) {
          MyClass[] arr = new MyClass[5];
          arr[0] = new MyClass();
          System.out.println(arr[0]);
          System.out.println(arr[0].toString());
          System.out.println(arr[1]);     // line 8
          System.out.println(arr[1].toString());     // line 9
class MyClass {
     public String toString() { return "my own implementation of toString"; }
When run produces...
my own implementation of toString
my own implementation of toString
null
java.lang.NullPointerException
     at ToString.main(ToString.java:9)
My question is why line 8 prints null, but line 9 does not. Well, the other way around really, I understand why line 9 produces an exception, but how does line 8 manage to produce null output?
I was under the impression that when an object is used in a println method that it's toString() method is invoked, if it doesn't have one then the toString() method on the Object class is invoked. If this is the case then surely line 8 is equivalent to line 9, unless java just sees the "." in line 9 against a null reference and throws it out because of that.
Thanks.

Answer 1

Because it actially calls String.valueOf(argument). Which is defined roughly as
public static String valueOf(Object object) {
    return object == null ? "null" : object.toString();