do not hide operation if selection is empty, fix issue #11

sampleModel/src/samplemodel/EachElementVersusTheRest.java

@@ -8,7 +8,7 @@
  * For a selection of <b>n</b> elements, will return <b>n</b> permutations each starting with
  * <b>selection[n]</b> element and followed by the rest of the elements. For example selection
  * [1,2,3] produces permutations [[1,2,3],[2,1,3],[3,1,2]]
- *
+ * 
  */
 public class EachElementVersusTheRest implements OperationInputPermutator
 {
@@ -18,16 +18,24 @@ public List<Object[]> getOperationInputPermutations(Object[] selection)
   {
 
     List<Object[]> permutations = new ArrayList<Object[]>();
-    for (Object o : selection)
+    // still needs to include one empty selection
+    if (selection.length == 0)
     {
-      List<Object> permutation = new ArrayList<>();
-      permutation.add(o);
+      permutations.add(selection);
+    }
+    else
+    {
+      for (Object o : selection)
+      {
+        List<Object> permutation = new ArrayList<>();
+        permutation.add(o);
 
-      List<Object> rest = new ArrayList<Object>(Arrays.asList(selection));
-      rest.remove(o);
-      permutation.addAll(rest);
+        List<Object> rest = new ArrayList<Object>(Arrays.asList(selection));
+        rest.remove(o);
+        permutation.addAll(rest);
 
-      permutations.add(permutation.toArray());
+        permutations.add(permutation.toArray());
+      }
     }
 
     return permutations;