node: Fix check that returned nil instead of an error string

node/pkg/governor/governor.go

@@ -794,8 +794,10 @@ func (gov *ChainGovernor) CheckPendingForTime(now time.Time) ([]*common.MessageP
 							// Mandatory check to ensure that the token should be able to reduce the Governor limit.
 							if tokenEntry.flowCancels {
 								if destinationChainEntry, ok := gov.chains[payload.TargetChain]; ok {
+									// Defense in depth check. A transfer with this value should have been
+									// added to the pending list above instead of reaching this branch.
 									if ce.isBigTransfer(value) {
-										return nil, err
+										return nil, fmt.Errorf("refusing to add flow cancel transfer with value %d above the bigTransactionSize %d", transfer.dbTransfer.Value, ce.bigTransactionSize)
 									}
 
 									if err := destinationChainEntry.addFlowCancelTransferFromDbTransfer(&dbTransfer); err != nil {