human
Solve the following python programming problem given the following code:
def merge_permissions(original, specified) : 
    ' Merge permissions together, and handle the ``ALL`` shortcut.
    ' 
    permissions = dict_list2set (original) 
    def _add(perm, identifier) : 
        permissions.setdefault (perm, set ()).add (identifier) 
def _discard(perm, identifier) : 
        permissions.setdefault (perm, set ()).discard (identifier) 
for (credentials_id, perms) in iteritems (specified) : 
        if ('-all' in [perm.lower () for perm in perms]) : 
            for perm in PERMISSIONS_SET : 
                _discard (perm, credentials_id) 
else : 
            if ('all' in [perm.lstrip ('+').lower () for perm in perms]) : 
                for perm in PERMISSIONS_SET : 
                    _add (perm, credentials_id) 
else : 
                for perm in [perm.lower () for perm in perms] : 
                    if perm.startswith ('-') : 
                        _discard (perm.lstrip ('-'), credentials_id) 
else : 
                        _add (perm.lstrip ('+'), perms) 
return dict_set2list (permissions) 

    
    

    Fix the buggy line: _add (perm.lstrip ('+'), perms)
assistant
#Here is Python code to fix the buggy line: _add (perm.

_add (perm.lstrip ('+'), credentials_id)