Fix protected branch for API (#24013)

Fix #23998

routers/api/v1/repo/branch.go

@@ -421,6 +421,10 @@ func CreateBranchProtection(ctx *context.APIContext) {
 	if ruleName == "" {
 		ruleName = form.BranchName //nolint
 	}
+	if len(ruleName) == 0 {
+		ctx.Error(http.StatusBadRequest, "both rule_name and branch_name are empty", "both rule_name and branch_name are empty")
+		return
+	}
 
 	isPlainRule := !git_model.IsRuleNameSpecial(ruleName)
 	var isBranchExist bool
@@ -502,7 +506,7 @@ func CreateBranchProtection(ctx *context.APIContext) {
 
 	protectBranch = &git_model.ProtectedBranch{
 		RepoID:                        ctx.Repo.Repository.ID,
-		RuleName:                      form.RuleName,
+		RuleName:                      ruleName,
 		CanPush:                       form.EnablePush,
 		EnableWhitelist:               form.EnablePush && form.EnablePushWhitelist,
 		EnableMergeWhitelist:          form.EnableMergeWhitelist,
@@ -534,7 +538,7 @@ func CreateBranchProtection(ctx *context.APIContext) {
 	}
 
 	if isBranchExist {
-		if err = pull_service.CheckPRsForBaseBranch(ctx.Repo.Repository, form.RuleName); err != nil {
+		if err = pull_service.CheckPRsForBaseBranch(ctx.Repo.Repository, ruleName); err != nil {
 			ctx.Error(http.StatusInternalServerError, "CheckPRsForBaseBranch", err)
 			return
 		}
@@ -552,7 +556,7 @@ func CreateBranchProtection(ctx *context.APIContext) {
 				}()
 			}
 			// FIXME: since we only need to recheck files protected rules, we could improve this
-			matchedBranches, err := git_model.FindAllMatchedBranches(ctx, ctx.Repo.GitRepo, form.RuleName)
+			matchedBranches, err := git_model.FindAllMatchedBranches(ctx, ctx.Repo.GitRepo, ruleName)
 			if err != nil {
 				ctx.Error(http.StatusInternalServerError, "FindAllMatchedBranches", err)
 				return
@@ -568,7 +572,7 @@ func CreateBranchProtection(ctx *context.APIContext) {
 	}
 
 	// Reload from db to get all whitelists
-	bp, err := git_model.GetProtectedBranchRuleByName(ctx, ctx.Repo.Repository.ID, form.RuleName)
+	bp, err := git_model.GetProtectedBranchRuleByName(ctx, ctx.Repo.Repository.ID, ruleName)
 	if err != nil {
 		ctx.Error(http.StatusInternalServerError, "GetProtectedBranchByID", err)
 		return