human
Solve the following python programming problem given the following code:
@ classmethod 
def from_v2(cls, case_block) : 
    '
        Gets a case update from a version 2 case. 
        Spec: https://github.com/dimagi/commcare/wiki/casexml20
        ' 
    def _to_attr(val) : 
        return ('@%s' % val) 
case_id_attr = _to_attr (const.CASE_TAG_ID) 
    if (case_id_attr not in case_block) : 
        raise CaseGenerationException ('No case_id attribute found in v2 case block, this is a required property.') 
user_id = case_block.get (_to_attr (const.CASE_TAG_USER_ID), '') 
    modified_on = case_block.get (_to_attr (const.CASE_TAG_MODIFIED), '') 
    return cls (id = case_block [case_id_attr], version = V2, block = case_id_attr, user_id = user_id, modified_on_str = modified_on) 

    
    

    Fix the buggy line: return cls (id = case_block [case_id_attr], version = V2, block = case_id_attr, user_id = user_id, modified_on_str = modified_on)
assistant
#Here is Python code to fix the buggy line: return cls (id = case_block [case_id_attr], version = V2, block = case_id_attr, user_id = user_id, modified_on_str = modified_on)
.

return cls (id = case_block [case_id_attr], version = V2, block = case_block, user_id = user_id, modified_on_str = modified_on)