re-use ForLoop elements without re-creating lists from scratch

src/main/java/com/hubspot/jinjava/lib/filter/SliceFilter.java

@@ -80,20 +80,26 @@ public Object filter(Object var, JinjavaInterpreter interpreter, String... args)
         args[0]
       );
     }
+
     List<List<Object>> result = new ArrayList<>();
+    List<Object> currentList = null; // lazy evaluation
 
-    List<Object> currentList = null;
     int i = 0;
     while (loop.hasNext()) {
-      Object next = loop.next();
       if (i % slices == 0) {
-        currentList = new ArrayList<>(slices);
-        result.add(currentList);
+        if (currentList != null) {
+          result.add(currentList);
+        }
+        currentList = new ArrayList<>();
       }
-      currentList.add(next);
+      currentList.add(loop.next());
       i++;
     }
 
+    if (currentList != null && !currentList.isEmpty()) {
+      result.add(currentList);
+    }
+
     if (args.length > 1 && currentList != null) {
       Object fillWith = args[1];
       while (currentList.size() < slices) {