 Complete the following phrase:  Although it did not become a constitutional requirement until 1977, it had been long-standing convention that a Senate casual vacancy be filled by a person from the same political party. However, on 27 February 1975, the Premier of New South Wales, Tom Lewis, controversially appointed Cleaver Bunton, a person with no political affiliations, to replace Murphy in the Senate, beginning the chain of events which led to the 