"The Flat Dictionary" task doesn't accept solution

"""I tested 3 solutions before. And i dont understand, how right solved it."""

def flatten(dictionary):
    stack = [((), dictionary)]
    result = {}
    while stack:
        path, current = stack.pop()
        for k,v in current.items():
            if isinstance(v, dict) and len(v)>=1:
                stack.append((path + (k,),v))
            else:
                result["/".join((path + (k,)))] = str(v).replace('{}',"")
    return result