diff --git a/pallets/attestation/src/mock.rs b/pallets/attestation/src/mock.rs
index 8b0d75226b..3eb90fdbb3 100644
--- a/pallets/attestation/src/mock.rs
+++ b/pallets/attestation/src/mock.rs
@@ -291,6 +291,7 @@ pub(crate) mod runtime {
 	}
 
 	impl ExtBuilder {
+		#[must_use]
 		pub fn with_delegation_hierarchies(
 			mut self,
 			delegation_hierarchies: DelegationHierarchyInitialization<Test>,
@@ -299,21 +300,25 @@ pub(crate) mod runtime {
 			self
 		}
 
+		#[must_use]
 		pub fn with_delegations(mut self, delegations: Vec<(TestDelegationNodeId, DelegationNode<Test>)>) -> Self {
 			self.delegations = delegations;
 			self
 		}
 
+		#[must_use]
 		pub fn with_ctypes(mut self, ctypes: Vec<(TestCtypeHash, CtypeCreatorOf<Test>)>) -> Self {
 			self.ctypes = ctypes;
 			self
 		}
 
+		#[must_use]
 		pub fn with_balances(mut self, balances: Vec<(AccountIdOf<Test>, BalanceOf<Test>)>) -> Self {
 			self.balances = balances;
 			self
 		}
 
+		#[must_use]
 		pub fn with_attestations(mut self, attestations: Vec<(TestClaimHash, AttestationDetails<Test>)>) -> Self {
 			self.attestations = attestations;
 			self
diff --git a/pallets/delegation/src/mock.rs b/pallets/delegation/src/mock.rs
index 8167aeb284..6be1a55f55 100644
--- a/pallets/delegation/src/mock.rs
+++ b/pallets/delegation/src/mock.rs
@@ -412,6 +412,7 @@ pub mod runtime {
 	}
 
 	impl ExtBuilder {
+		#[must_use]
 		pub fn with_delegation_hierarchies(
 			mut self,
 			delegation_hierarchies: DelegationHierarchyInitialization<Test>,
@@ -420,16 +421,19 @@ pub mod runtime {
 			self
 		}
 
+		#[must_use]
 		pub fn with_balances(mut self, balances: Vec<(AccountIdOf<Test>, BalanceOf<Test>)>) -> Self {
 			self.balances = balances;
 			self
 		}
 
+		#[must_use]
 		pub fn with_ctypes(mut self, ctypes: Vec<(TestCtypeHash, SubjectId)>) -> Self {
 			self.ctypes = ctypes;
 			self
 		}
 
+		#[must_use]
 		pub fn with_delegations(mut self, delegations: Vec<(TestDelegationNodeId, DelegationNode<Test>)>) -> Self {
 			self.delegations_stored = delegations;
 			self
diff --git a/pallets/parachain-staking/src/lib.rs b/pallets/parachain-staking/src/lib.rs
index bca68d2188..dabc1bdcd0 100644
--- a/pallets/parachain-staking/src/lib.rs
+++ b/pallets/parachain-staking/src/lib.rs
@@ -1485,7 +1485,7 @@ pub mod pallet {
 			ensure!(amount >= T::MinDelegatorStake::get(), Error::<T>::NomStakeBelowMin);
 
 			// cannot be a collator candidate and delegator with same AccountId
-			ensure!(!Self::is_active_candidate(&acc).is_some(), Error::<T>::CandidateExists);
+			ensure!(Self::is_active_candidate(&acc).is_none(), Error::<T>::CandidateExists);
 			ensure!(
 				Unstaking::<T>::get(&acc).len().saturated_into::<u32>() < T::MaxUnstakeRequests::get(),
 				Error::<T>::CannotJoinBeforeUnlocking
@@ -2139,8 +2139,7 @@ pub mod pallet {
 		) -> Option<(BalanceOf<T>, BalanceOf<T>)> {
 			top_candidates
 				.get(index)
-				.map(|stake| CandidatePool::<T>::get(&stake.owner))
-				.flatten()
+				.and_then(|stake| CandidatePool::<T>::get(&stake.owner))
 				// SAFETY: the total is always more than the stake
 				.map(|state| (state.stake, state.total - state.stake))
 		}
diff --git a/pallets/parachain-staking/src/tests.rs b/pallets/parachain-staking/src/tests.rs
index 8a1f3baefe..f9ead1d482 100644
--- a/pallets/parachain-staking/src/tests.rs
+++ b/pallets/parachain-staking/src/tests.rs
@@ -887,7 +887,7 @@ fn execute_leave_candidates_with_delay() {
 					*collator
 				));
 				assert!(StakePallet::candidate_pool(&collator).is_none());
-				assert!(!StakePallet::is_active_candidate(collator).is_some());
+				assert!(StakePallet::is_active_candidate(collator).is_none());
 				assert_eq!(StakePallet::unstaking(collator).len(), 1);
 			}
 			assert_eq!(CandidatePool::<Test>::count(), 5, "Five collators left.");
@@ -906,7 +906,7 @@ fn execute_leave_candidates_with_delay() {
 					collator
 				));
 				assert!(StakePallet::candidate_pool(&collator).is_none());
-				assert!(!StakePallet::is_active_candidate(&collator).is_some());
+				assert!(StakePallet::is_active_candidate(&collator).is_none());
 				assert_eq!(StakePallet::unstaking(collator).len(), 1);
 			}
 			assert_eq!(CandidatePool::<Test>::count(), 2, "3 collators left.");
diff --git a/rust-toolchain.toml b/rust-toolchain.toml
index 810eebdb05..fb3e5de512 100644
--- a/rust-toolchain.toml
+++ b/rust-toolchain.toml
@@ -1,3 +1,3 @@
 [toolchain]
-channel = "nightly-2021-11-08"
+channel = "nightly-2022-01-08"
 targets = [ "wasm32-unknown-unknown" ]