private Map<String, Capacity> add(Map<String, Capacity> from, Map<String, Capacity> to) {
        if (to == null)
            return clone(from);
        if (from != null) {
            for (Map.Entry<String, Capacity> entryFrom : from.entrySet()) {
                final String key = entryFrom.getKey();
                final Capacity tocap = to.get(key);
                final Capacity fromcap = entryFrom.getValue();
                if (tocap == null) {
                    to.put(key, clone(fromcap));
                } else {
                    to.put(key, new Capacity().withCapacityUnits(
                        doubleOf(tocap) + doubleOf(fromcap)));
                }
            }
        }
        return to;
    }
A collection of <code>Item</code>'s.

An <code>ItemCollection</code> object maintains a cursor pointing to its
current pages of data. Initially the cursor is positioned before the first page.
The next method moves the cursor to the next row, and because it returns
false when there are no more rows in the <code>ItemCollection</code> object,
it can be used in a while loop to iterate through the collection.

Network calls can be triggered when the collection is iterated across page
boundaries.

@param <R> low level result type
aws-java-sdk-dynamodb/src/main/java/com/amazonaws/services/dynamodbv2/document/ItemCollection.java