title: String constructor with null value
body: <p>why String (String) constructor with null value cause compile-time error? I think there is 2+ constructor that takes Object and when init. it with null it doesn't know which to start. I'm wonder if there is another reason</p>
  
  <pre><code>String s = new String(null); // compile time error
  
  
  StringBuffer sb = new StringBuffer(null); // no error
  </code></pre>