<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def ResultCollectionForFID(cls, flow_id):
 """Returns the ResultCollection for the flow with a given flow_id. Args: flow_id: The id of the flow, a RDFURN of the form aff4:/flows/F:123456. Returns: The collection containing the results for the flow identified by the id. """

    # TODO: Disallow/remove URNs after migration.
    if not isinstance(flow_id, rdfvalue.RDFURN):
      flow_id = rdfvalue.RDFURN(flow_id)

    return sequential_collection.GeneralIndexedCollection(
        flow_id.Add(RESULTS_SUFFIX))