[v1.3.x] Bug 1921458: run bundle-upgrade should handle error gracef…

…ully when a previous operator version doesn't exist (#4451)

* `run bundle-upgrade` command will handle error gracefully if the previous operator version doesn't exist in the cluster

Signed-off-by: rashmigottipati <chowdary.grashmi@gmail.com>

changelog/fragments/bugfix-run-bundle-upgrade.yaml

@@ -0,0 +1,4 @@
+entries:
+  - description: >
+      `run bundle-upgrade` handles error gracefully when a previous operator version doesn't exist
+    kind: bugfix

internal/olm/operator/registry/operator_installer.go

@@ -16,6 +16,7 @@ package registry
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"time"
 
@@ -108,6 +109,11 @@ func (o OperatorInstaller) UpgradeOperator(ctx context.Context) (*v1alpha1.Clust
 		return nil, fmt.Errorf("error getting list of subscriptions: %v", err)
 	}
 
+	// If there are no subscriptions found, then the previous operator version doesn't exist, so return error
+	if len(subList.Items) == 0 {
+		return nil, errors.New("no existing operator found in the cluster to upgrade")
+	}
+
 	var subscription *v1alpha1.Subscription
 	for i := range subList.Items {
 		s := subList.Items[i]