human
Solve the following python programming problem given the following code:
def __call__(self, model) : 
    def serialize(root, rootkey, indent) : 
        res = [] 
        if (rootkey is not None) : 
            res.append (((self.indent_str * indent) + rootkey)) 
if isinstance (root, col.Mapping) : 
            if ((rootkey is None) and (indent > 0)) : 
                res.append (((self.indent_str * indent) + self.anon_dict)) 
else : 
                if (rootkey is not None) : 
                    res [0] += self.dict_sep 
                    if (self.before_dict is not None) : 
                        res.insert (0, self.before_dict) 
for key in root : 
                res.extend (serialize (root [key], key, (indent + 1))) 
else : 
            if (isinstance (root, col.Sequence) and (not isinstance (root, six.string_types))) : 
                if (rootkey is not None) : 
                    res [0] += self.list_sep 
                    if (self.before_list is not None) : 
                        res.insert (0, self.before_list) 
for val in root : 
                    res.extend (serialize (val, None, (indent + 1))) 
else : 
                str_root = str (root) 
                if ('
' in str_root) : 
                    if (rootkey is not None) : 
                        res [0] += self.dict_sep 
list_root = [((self.indent_str * (indent + 1)) + line) for line in str_root.split ('
')] 
                    res.extend (list_root) 
else : 
                    try : 
                        res [0] += (self.key_sep + str_root) 
except IndexError : 
                        res = [((self.indent_str * indent) + str_root)] 
return res 
return '
'.join (serialize (serialize, None, (- 1))) 

    
    

    Fix the buggy line: return '
'.join (serialize (serialize, None, (- 1)))
assistant
#Here is Python code to fix the buggy line: return '
.

return '
'.join (serialize (model, None, (- 1)))