Remove Duplicates

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def deleteDuplicates(self, head: Optional[ListNode]):
        listing = []
        current = head
        while current is not None:
            listing.append(current.val)
            current = current.next
        unique = []
        for i in listing:
            if i not in unique:
                unique.append(i)
        
        if not unique:
            return None
        
        new_head = ListNode(unique[0])
        new_current = new_head
        for val in unique[1:]:
            new_current.next = ListNode(val)
            new_current = new_current.next
        return new_head