def AR_8(dul):
    """Association release AR-8.

    On receiving association release request while local is requesting release
    then issue release collision indication

    State-event triggers: Sta7 + Evt12

    References
    ----------
    1. DICOM Standard 2015b, PS3.8, Table 9-7, "Associate Establishment
       Related Actions"

    Parameters
    ----------
    dul : pynetdicom.dul.DULServiceProvider
        The DICOM Upper Layer Service instance for the local AE

    Returns
    -------
    str
        Either Sta9 or Sta10, the next state of the state machine
    """
    dul.to_user_queue.put(dul.primitive)
    if dul.assoc.is_requestor:
        return 'Sta9'
    return 'Sta10'
