Why StringBuilder throws NullPointerException
<p>This question may be redundant but I really don't understand why the following code throws: <code>Exception in thread "main" java.lang.NullPointerException</code></p>

<pre><code>public class NewClass {
    static StringBuilder SB;
    public static void main(String[] args) {
        SB.append("Tesing");
        System.out.println(SB);
    }

}
</code></pre>