title: java.lang.IllegalArgumentException: invalid ObjectId [0]
body: <p>I'm getting an java.lang.IllegalArgumentException: invalid ObjectId [0] when I try to do similar to the code below in one of my class.</p>
  
  <pre><code>    String s = "0_abc";
  --------
  private ObjectId obj; [Instance variable]
  public NewClass(String s){
      String[] sarray = s.split("_");
      obj = new ObjectId(sarray[0]);
  }
  </code></pre>
  
  <p>What could be the possible reason for it to fail?</p>