@Override
    public String toString() {
      return String.format("startingOffset: %s, endingOffset: %s", startingOffset, endingOffset);
    }
Starting offset must be non-null, and a non-null ending offset must be equal to or greater than starting offset.

If ending offset == null (e.g. empty topic) or starting offset == ending offset, we should trim everything
from starting to head. E.g. to trim entire changelog, restore offsets == (oldest, null).
samza-core/src/main/java/org/apache/samza/storage/TransactionalStateTaskRestoreManager.java