chore(*): enable nilnil linter (#401)

enable `nilnil` linter

Signed-off-by: Soren Yang <[email protected]>

.golangci.yaml

@@ -41,7 +41,7 @@ linters:
     # - gosec
     - nakedret
     - nilerr
-    # - nilnil
+    - nilnil
     # - noctx
     - nolintlint
     - prealloc

server/kv/db.go

@@ -526,7 +526,7 @@ func checkExpectedVersionId(batch WriteBatch, key string, expectedVersionId *int
 		if errors.Is(err, ErrKeyNotFound) {
 			if expectedVersionId == nil || *expectedVersionId == -1 {
 				// OK, we were checking that the key was not there, and it's indeed not there
-				return nil, nil
+				return nil, nil //nolint:nilnil
 			} else {
 				return nil, ErrBadVersionId
 			}

server/quorum_ack_tracker.go

@@ -178,7 +178,7 @@ func (q *quorumAckTracker) WaitForCommitOffset(ctx context.Context, offset int64
 		return f()
 	}
 
-	return nil, nil
+	return nil, nil //nolint:nilnil
 }
 
 func (q *quorumAckTracker) Close() error {

server/quorum_ack_tracker_test.go

@@ -190,7 +190,7 @@ func TestQuorumAckTracker_WaitForCommitOffset(t *testing.T) {
 
 	go func() {
 		_, err := at.WaitForCommitOffset(context.Background(), 2, func() (*proto.WriteResponse, error) {
-			return nil, nil
+			return nil, nil //nolint:nilnil
 		})
 		ch <- err
 	}()