The investment seeks to track the investment results of the S&P AMT-Free Municipal Series Callable-Adjusted Dec 2028 IndexTM. The index measures the performance of investment-grade (as determined by S&P Dow Jones Indices LLC), non-callable and callable U.S. municipal bonds expected to mature or be redeemed after December 31, 2027 and prior to December 2, 2028. The fund generally will invest at least 90% of its assets in the component securities of the index and may invest up to 10% of its assets in certain futures, options and swap contracts, cash and cash equivalents. The fund is non-diversified.