fix(bitbucketdatacenter): ignore branch deletion events in ParsePayload

When a branch is deleted in Bitbucket Data Center, the repo:refs_changed
webhook sends a change with toHash set to all-zeros. Previously, Pipelines
as Code treated this like a push event, which caused errors when trying
to validate a missing commit.

This patch detects and ignores such events early in ParsePayload.

Fixes #2035

Author: infernus01

pkg/provider/bitbucketdatacenter/parse_payload.go

@@ -155,6 +155,11 @@ func (v *Provider) ParsePayload(_ context.Context, _ *params.Run, request *http.
 		}
 		v.pullRequestNumber = e.PullRequest.ID
 	case *types.PushRequestEvent:
+		for _, change := range e.Changes {
+			if change.ToHash == "0000000000000000000000000000000000000000" && change.Type == "DELETE" {
+				return nil, nil
+			}
+		}
 		processedEvent.TriggerTarget = triggertype.Push
 		processedEvent.EventType = triggertype.Push.String()
 		processedEvent.Organization = e.Repository.Project.Key

pkg/provider/bitbucketdatacenter/parse_payload_test.go

@@ -660,6 +660,18 @@ func TestParsePayload(t *testing.T) {
 			payloadEvent: bbv1test.MakePREvent(ev1, "/cancel"),
 			expEvent:     ev1,
 		},
+		{
+			name:      "deleted branch should be ignored",
+			eventType: "repo:refs_changed",
+			payloadEvent: bbv1test.MakePushEvent(ev1, []types.PushRequestEventChange{
+				{
+					ToHash: "0000000000000000000000000000000000000000",
+					RefID:  "refs/heads/feature-branch",
+					Type:   "DELETE",
+				},
+			}),
+			expEvent: nil,
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -685,7 +697,12 @@ func TestParsePayload(t *testing.T) {
 				return
 			}
 			assert.NilError(t, err)
-
+			if tt.expEvent == nil {
+				if got != nil {
+					t.Fatalf("expected event to be nil, got: %+v", got)
+				}
+				return
+			}
 			assert.Equal(t, got.AccountID, tt.expEvent.AccountID)
 
 			// test that we got slashed