Enable nilnil linter for new code (#36591)

Fixes: https://github.com/go-gitea/gitea/issues/36152

Enable the `nilnil` linter while adding `//nolint` comments to existing
violations. This will ensure no new issues enter the code base while we
can fix existing issues gradually.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

models/activities/action_list.go

@@ -30,7 +30,7 @@ func (actions ActionList) getUserIDs() []int64 {
 
 func (actions ActionList) LoadActUsers(ctx context.Context) (map[int64]*user_model.User, error) {
 	if len(actions) == 0 {
-		return nil, nil
+		return nil, nil //nolint:nilnil // returns nil when there are no actions
 	}
 
 	userIDs := actions.getUserIDs()

models/asymkey/gpg_key_commit_verification.go

@@ -70,7 +70,7 @@ func hashAndVerify(sig *packet.Signature, payload string, k *GPGKey) (*GPGKey, e
 	// We will ignore errors in verification as they don't need to be propagated up
 	err = verifySign(sig, hash, k)
 	if err != nil {
-		return nil, nil
+		return nil, nil //nolint:nilnil // verification failed, not an error
 	}
 	return k, nil
 }
@@ -86,7 +86,7 @@ func hashAndVerifyWithSubKeys(sig *packet.Signature, payload string, k *GPGKey)
 			return verified, err
 		}
 	}
-	return nil, nil
+	return nil, nil //nolint:nilnil // verification failed, not an error
 }
 
 func HashAndVerifyWithSubKeysCommitVerification(sig *packet.Signature, payload string, k *GPGKey, committer, signer *user_model.User, email string) *CommitVerification {

models/auth/oauth2.go

@@ -209,7 +209,7 @@ func (app *OAuth2Application) GetGrantByUserID(ctx context.Context, userID int64
 	if has, err := db.GetEngine(ctx).Where("user_id = ? AND application_id = ?", userID, app.ID).Get(grant); err != nil {
 		return nil, err
 	} else if !has {
-		return nil, nil
+		return nil, nil //nolint:nilnil // return nil to indicate that the object does not exist
 	}
 	return grant, nil
 }
@@ -431,13 +431,13 @@ func GetOAuth2AuthorizationByCode(ctx context.Context, code string) (auth *OAuth
 	if has, err := db.GetEngine(ctx).Where("code = ?", code).Get(auth); err != nil {
 		return nil, err
 	} else if !has {
-		return nil, nil
+		return nil, nil //nolint:nilnil // return nil to indicate that the object does not exist
 	}
 	auth.Grant = new(OAuth2Grant)
 	if has, err := db.GetEngine(ctx).ID(auth.GrantID).Get(auth.Grant); err != nil {
 		return nil, err
 	} else if !has {
-		return nil, nil
+		return nil, nil //nolint:nilnil // return nil to indicate that the object does not exist
 	}
 	return auth, nil
 }
@@ -521,7 +521,7 @@ func GetOAuth2GrantByID(ctx context.Context, id int64) (grant *OAuth2Grant, err
 	if has, err := db.GetEngine(ctx).ID(id).Get(grant); err != nil {
 		return nil, err
 	} else if !has {
-		return nil, nil
+		return nil, nil //nolint:nilnil // return nil to indicate that the object does not exist
 	}
 	return grant, err
 }

models/db/collation.go

@@ -98,7 +98,7 @@ func CheckCollations(x *xorm.Engine) (*CheckCollationsResult, error) {
 			return nil, err
 		}
 	} else {
-		return nil, nil
+		return nil, nil //nolint:nilnil // return nil for unsupported database types
 	}
 
 	if res.DatabaseCollation == "" {

models/dbfs/dbfile.go

@@ -339,7 +339,7 @@ func findFileMetaByID(ctx context.Context, metaID int64) (*dbfsMeta, error) {
 	} else if ok {
 		return &fileMeta, nil
 	}
-	return nil, nil
+	return nil, nil //nolint:nilnil // return nil to indicate that the object does not exist
 }
 
 func buildPath(path string) string {

models/git/lfs_lock.go

@@ -130,7 +130,7 @@ func GetLFSLockByRepoID(ctx context.Context, repoID int64, page, pageSize int) (
 // GetTreePathLock returns LSF lock for the treePath
 func GetTreePathLock(ctx context.Context, repoID int64, treePath string) (*LFSLock, error) {
 	if !setting.LFS.StartServer {
-		return nil, nil
+		return nil, nil //nolint:nilnil // return nil when LFS is not started
 	}
 
 	locks, err := GetLFSLockByRepoID(ctx, repoID, 0, 0)
@@ -142,7 +142,7 @@ func GetTreePathLock(ctx context.Context, repoID int64, treePath string) (*LFSLo
 			return lock, nil
 		}
 	}
-	return nil, nil
+	return nil, nil //nolint:nilnil // return nil to indicate that the object does not exist
 }
 
 // CountLFSLockByRepoID returns a count of all LFSLocks associated with a repository.

models/git/protected_branch.go

@@ -318,7 +318,7 @@ func GetProtectedBranchRuleByName(ctx context.Context, repoID int64, ruleName st
 	if err != nil {
 		return nil, err
 	} else if !exist {
-		return nil, nil
+		return nil, nil //nolint:nilnil // return nil to indicate that the object does not exist
 	}
 	return rel, nil
 }
@@ -329,7 +329,7 @@ func GetProtectedBranchRuleByID(ctx context.Context, repoID, ruleID int64) (*Pro
 	if err != nil {
 		return nil, err
 	} else if !exist {
-		return nil, nil
+		return nil, nil //nolint:nilnil // return nil to indicate that the object does not exist
 	}
 	return rel, nil
 }

models/git/protected_tag.go

@@ -104,7 +104,7 @@ func GetProtectedTagByID(ctx context.Context, id int64) (*ProtectedTag, error) {
 		return nil, err
 	}
 	if !has {
-		return nil, nil
+		return nil, nil //nolint:nilnil // return nil to indicate that the object does not exist
 	}
 	return tag, nil
 }
@@ -117,7 +117,7 @@ func GetProtectedTagByNamePattern(ctx context.Context, repoID int64, pattern str
 		return nil, err
 	}
 	if !has {
-		return nil, nil
+		return nil, nil //nolint:nilnil // return nil to indicate that the object does not exist
 	}
 	return tag, nil
 }

models/issues/issue.go

@@ -498,7 +498,7 @@ func (issue *Issue) GetLastComment(ctx context.Context) (*Comment, error) {
 		return nil, err
 	}
 	if !exist {
-		return nil, nil
+		return nil, nil //nolint:nilnil // return nil to indicate that the object does not exist
 	}
 	return &c, nil
 }

models/issues/review.go

@@ -384,7 +384,7 @@ func CreateReview(ctx context.Context, opts CreateReviewOptions) (*Review, error
 // GetCurrentReview returns the current pending review of reviewer for given issue
 func GetCurrentReview(ctx context.Context, reviewer *user_model.User, issue *Issue) (*Review, error) {
 	if reviewer == nil {
-		return nil, nil
+		return nil, nil //nolint:nilnil // return nil when reviewer is nil
 	}
 	reviews, err := FindReviews(ctx, FindReviewOptions{
 		Types:      []ReviewType{ReviewTypePending},

models/organization/org_user.go

@@ -174,13 +174,13 @@ func GetOrgAssignees(ctx context.Context, orgID int64) (_ []*user_model.User, er
 
 func loadOrganizationOwners(ctx context.Context, users user_model.UserList, orgID int64) (map[int64]*TeamUser, error) {
 	if len(users) == 0 {
-		return nil, nil
+		return nil, nil //nolint:nilnil // return nil when there are no users
 	}
 	ownerTeam, err := GetOwnerTeam(ctx, orgID)
 	if err != nil {
 		if IsErrTeamNotExist(err) {
 			log.Error("Organization does not have owner team: %d", orgID)
-			return nil, nil
+			return nil, nil //nolint:nilnil // return nil when owner team does not exist
 		}
 		return nil, err
 	}

models/repo/archiver.go

@@ -107,7 +107,7 @@ func GetRepoArchiver(ctx context.Context, repoID int64, tp ArchiveType, commitID
 	if has {
 		return &archiver, nil
 	}
-	return nil, nil
+	return nil, nil //nolint:nilnil // return nil to indicate that the object does not exist
 }
 
 // ExistsRepoArchiverWithStoragePath checks if there is a RepoArchiver for a given storage path

models/repo/fork.go

@@ -49,7 +49,7 @@ func GetUserFork(ctx context.Context, repoID, userID int64) (*Repository, error)
 		return nil, err
 	}
 	if !has {
-		return nil, nil
+		return nil, nil //nolint:nilnil // return nil to indicate that the object does not exist
 	}
 	return &forkedRepo, nil
 }

models/repo/repo.go

@@ -878,7 +878,7 @@ func IsRepositoryModelExist(ctx context.Context, u *user_model.User, repoName st
 // non-generated repositories, and TemplateRepo will be left untouched)
 func GetTemplateRepo(ctx context.Context, repo *Repository) (*Repository, error) {
 	if !repo.IsGenerated() {
-		return nil, nil
+		return nil, nil //nolint:nilnil // return nil for non-generated repositories
 	}
 
 	return GetRepositoryByID(ctx, repo.TemplateID)

models/repo/topic.go

@@ -257,7 +257,7 @@ func DeleteTopic(ctx context.Context, repoID int64, topicName string) (*Topic, e
 	}
 	if topic == nil {
 		// Repo doesn't have topic, can't be removed
-		return nil, nil
+		return nil, nil //nolint:nilnil // return nil to indicate that the topic does not exist
 	}
 
 	return db.WithTx2(ctx, func(ctx context.Context) (*Topic, error) {

models/unittest/fixtures_loader.go

@@ -169,7 +169,7 @@ func (f *fixturesLoaderInternal) Load() error {
 
 func FixturesFileFullPaths(dir string, files []string) (map[string]*FixtureItem, error) {
 	if files != nil && len(files) == 0 {
-		return nil, nil // load nothing
+		return nil, nil //nolint:nilnil // load nothing
 	}
 	files = slices.Clone(files)
 	if len(files) == 0 {

models/unittest/fixtures_test.go

@@ -16,7 +16,7 @@ import (
 )
 
 var NewFixturesLoaderVendor = func(e *xorm.Engine, opts unittest.FixturesOptions) (unittest.FixturesLoader, error) {
-	return nil, nil
+	return nil, nil //nolint:nilnil // no vendor fixtures loader configured
 }
 
 /*

models/user/block.go

@@ -90,7 +90,7 @@ func GetBlocking(ctx context.Context, blockerID, blockeeID int64) (*Blocking, er
 		return nil, err
 	}
 	if len(blocks) == 0 {
-		return nil, nil
+		return nil, nil //nolint:nilnil // return nil to indicate that the object does not exist
 	}
 	return blocks[0], nil
 }

models/user/email_address.go

@@ -215,7 +215,7 @@ func GetEmailAddressByID(ctx context.Context, uid, id int64) (*EmailAddress, err
 	if has, err := db.GetEngine(ctx).ID(id).Get(email); err != nil {
 		return nil, err
 	} else if !has {
-		return nil, nil
+		return nil, nil //nolint:nilnil // return nil to indicate that the object does not exist
 	}
 	return email, nil
 }

models/user/list.go

@@ -48,7 +48,7 @@ func (users UserList) GetTwoFaStatus(ctx context.Context) map[int64]bool {
 
 func (users UserList) loadTwoFactorStatus(ctx context.Context) (map[int64]*auth.TwoFactor, error) {
 	if len(users) == 0 {
-		return nil, nil
+		return nil, nil //nolint:nilnil // returns nil when there are no users
 	}
 
 	userIDs := users.GetUserIDs()

models/user/user.go

@@ -1193,7 +1193,7 @@ func (eum *EmailUserMap) GetByEmail(email string) *User {
 
 func GetUsersByEmails(ctx context.Context, emails []string) (*EmailUserMap, error) {
 	if len(emails) == 0 {
-		return nil, nil
+		return nil, nil //nolint:nilnil // return nil when there are no emails to look up
 	}
 
 	needCheckEmails := make(container.Set[string])