How to use the pynetdicom.PDU.ImplementationClassUIDSubItem function in pynetdicom

def ImplementationClassUID(self):
        """
        See PS3.7 D3.3.2
        
        Mandatory
        
        Returns
        -------
        pydicom.uid.UID
            Association Requestor's ImplementationClassUID
        """
        for ii in self.UserData:
            if isinstance(ii, ImplementationClassUIDSubItem):
                return UID(ii.ImplementationClassUID.decode('utf-8'))

def NextSubItemType(Stream):
    """
    Parameters
    ----------
    Stream - ?
        ???
        
    Returns
    -------
    sub_item
        The PDU sub item type
    """
    ItemType = NextType(Stream)
    if ItemType == 0x52:
        return ImplementationClassUIDSubItem
    elif ItemType == 0x51:
        return MaximumLengthSubItem
    elif ItemType == 0x55:
        return ImplementationVersionNameSubItem
    elif ItemType == 0x53:
        return AsynchronousOperationsWindowSubItem
    elif ItemType == 0x54:
        return SCP_SCU_RoleSelectionSubItem
    elif ItemType == 0x56:
        return SOPClassExtentedNegociationSubItem
    elif ItemType is None:
        return None
    else:
        raise #'Invalid Sub Item', "0x%X" % ItemType

def ToParams(self):
        tmp = ImplementationClassUIDSubItem()
        tmp.FromParams(self)
        return tmp

elif item_type == 0x07:
        return A_ABORT_PDU()
    elif item_type == 0x10:
        return ApplicationContextItem()
    elif item_type == 0x20:
        return PresentationContextItemRQ()
    elif item_type == 0x21:
        return PresentationContextItemAC()
    elif item_type == 0x30:
        return AbstractSyntaxSubItem()
    elif item_type == 0x40:
        return TransferSyntaxSubItem()
    elif item_type == 0x50:
        return UserInformationItem()
    elif item_type == 0x52:
        return ImplementationClassUIDSubItem()
    elif item_type == 0x51:
        return MaximumLengthSubItem()
    elif item_type == 0x55:
        return ImplementationVersionNameSubItem()
    elif item_type == 0x53:
        return AsynchronousOperationsWindowSubItem()
    elif item_type == 0x54:
        return SCP_SCU_RoleSelectionSubItem()
    elif item_type == 0x56:
        return SOPClassExtendedNegotiationSubItem()
    elif item_type is None:
        # if we are at the end of stream
        return None
    else:
        raise ValueError("During PDU decoding we received an invalid "
                    "PDU type: %s" %pdu_type)