Given a list of integers values, your job is to return the sum of the values; however, if the same integer value appears multiple times in the list, you can only count it once in your sum.

For example:
```python
[ 1, 2, 3] ==> 6

[ 1, 3, 8, 1, 8] ==> 12

[ -1, -1, 5, 2, -7] ==> -1

[] ==> None
```

Good Luck!

Difficulty: introductory

Starter code:

def unique_sum(lst):
	

Solutions:
def unique_sum(lst):
    return sum(set(lst)) if lst else None


def unique_sum(lst):
    if lst:
       return sum(set(lst)) 

def unique_sum(lst):
    s = set(lst)
    
    return sum(s) if len(s) != 0 else None

unique_sum = lambda l: sum(set(l)) if l else None

def unique_sum(lst):
    if lst:
        return sum(set(lst))
    else:
        return None


def unique_sum(lst):
    return sum(set(lst)) if len(lst) > 0 else None

def unique_sum(lst):
    new_lst = []
    for i in lst:
        if not i in new_lst:
            new_lst.append(i)
    return sum(new_lst) if lst else None

def unique_sum(lst):
    return sum(set(lst)) if len(set(lst)) > 0 else None

def unique_sum(lst):
    y=lambda x:sum(set(x))
    if len(lst)==0:
        return None
    elif y(lst)==0:
        return 0
    else:
        return y(lst)

def unique_sum(lst):
    
    if lst==[]:
        
        return None
    
    else:
        
        s = set(lst)
    
        v = list(s)
    
        d = sum(v)
    
        return d