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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 getOldestRequestTime(self):
 """Returns the submitted_at of the oldest unclaimed build request for this builder, or None if there are no build requests. @returns: datetime instance or None, via Deferred """

        bldrid = yield self.getBuilderId()
        unclaimed = yield self.master.data.get(
            ('builders', bldrid, 'buildrequests'),
            [resultspec.Filter('claimed', 'eq', [False])],
            order=['submitted_at'], limit=1)
        if unclaimed:
            return unclaimed[0]['submitted_at']