title: weka EuclideanDistance
body: <p>I have following code to calculate the EuclideanDistance distance using weka.core.EuclideanDistance, where both two instances are all missing values, like below 
  <p>Instance first are all missing values: ?,?,?,?
  <p>instance second are all missing values:?,?,?,?</p>
  
  <pre><code>EuclideanDistance distance = new EuclideanDistance();
  distance.setInstances(test);
  Instance first = test.get(0);
  Instance second = test.get(1);
  double d = distance.distance(first, second);
  </code></pre>
  
  <p>however, when i run the code, i got the result is 4.0, i have no idea where is this 4.0 from,can anyone tell me? Thanks in advance!</p>