ADD: improved nearest child retrieval

src/mhtree/InternalNode.java

@@ -5,7 +5,9 @@ import messif.objects.LocalAbstractObject;
 
 import java.io.Serializable;
 import java.util.Collection;
+import java.util.Comparator;
 import java.util.List;
+import java.util.Optional;
 import java.util.stream.Collectors;
 
 /**
@@ -42,19 +44,11 @@ class InternalNode extends Node implements Serializable {
      * @return the nearest child to the {@code object}
      */
     protected Node getNearestChild(LocalAbstractObject object) {
-        Node nearestChild = children.get(0);
-        double minDistance = nearestChild.getDistance(object);
-
-        for (int i = 1; i < children.size(); i++) {
-            double distance = children.get(i).getDistance(object);
-
-            if (distance < minDistance) {
-                minDistance = distance;
-                nearestChild = children.get(i);
-            }
-        }
+        Optional<Node> nearestChild = children
+                .stream()
+                .min(Comparator.comparing(child -> child.getDistance(object)));
 
-        return nearestChild;
+        return nearestChild.orElseThrow(() -> new IllegalStateException("Internal node has no children"));
     }
 
     /**