from typing import Iterable
from typing import List
from typing import Optional


def sorted_dedup(iterable: Iterable) -> List[Optional[int]]:
    """Sorted deduplication without removing the
    possibly duplicated `None` values."""
    dedup: List[Optional[int]] = []

    visited = set()
    for item in iterable:
        if item is None:
            dedup.append(item)
        elif item not in visited:
            dedup.append(item)
            visited.add(item)

    return dedup