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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _master_key_provider() -> KMSMasterKeyProvider: """Build the V0 master key provider."""

    master_key_provider = KMSMasterKeyProvider()
    master_key_provider.add_master_key_provider(NullMasterKey())
    master_key_provider.add_master_key_provider(CountingMasterKey())
    return master_key_provider