Fixes several inaccurate Tuple hints; Keep at_periods checking for None.

nucypher/blockchain/eth/agents.py

@@ -341,7 +341,7 @@ class StakingEscrowAgent(EthereumContractAgent):
 
         Returns an amount of NuNits.
         """
-        if not at_period:
+        if at_period is None:  # allow 0, vs default
             # Get the current period on-chain by default.
             at_period = self.contract.functions.getCurrentPeriod().call()
         return NuNits(self.contract.functions.lockedPerPeriod(at_period).call())

nucypher/types.py

@@ -92,6 +92,6 @@ class StakerInfo(NamedTuple):
     worker_start_period: Period
     worker: ChecksumAddress
     flags: int
-    downtime: Tuple[Downtime]
-    substake_info: Tuple[RawSubStakeInfo]
-    history: Tuple[int]
+    downtime: Tuple[Downtime, ...]
+    substake_info: Tuple[RawSubStakeInfo, ...]
+    history: Tuple[int, ...]