ADD: validation checks on MH-Tree params

src/mhtree/MHTree.java

@@ -288,6 +288,22 @@ public class MHTree extends Algorithm implements Serializable {
         private Node root;
 
         public Builder(List<LocalAbstractObject> objects, int bucketCapacity, int arity) {
+            if (objects == null) {
+                throw new NullPointerException("List of objects is null");
+            }
+
+            if (objects.size() < 3) {
+                throw new IllegalArgumentException("Number of objects cannot by smaller than 3");
+            }
+
+            if (bucketCapacity < 3) {
+                throw new IllegalArgumentException("Bucket capacity cannot be smaller than 3");
+            }
+
+            if (arity < 2) {
+                throw new IllegalArgumentException("Arity cannot be smaller than 2");
+            }
+
             this.objects = objects;
             this.bucketCapacity = bucketCapacity;
             this.arity = arity;