To implement array growth, Value::resize must create new empty array elements.
It does not do this completely. It only makes the last element. The interior elements of the array are left unpopulated.

The .size() will be reported to the expected value because that only looks at the key of the final element of the map, but this is misleading because the array is sparse. The sparseness is a clever optimization but iteration over the sparse array doesn't behave as expected. The sparse elements are just skipped by the iterator sequence.

• OS: MacOS

Discovered while investigating #1253