Improve handling of alerts when no active alerts are present

internal/adapters/weatherapi/client.go

@@ -202,13 +202,18 @@ func (b *bundleBuilder) fetchNarrative(ctx context.Context) error {
 }
 
 func (b *bundleBuilder) fetchAlerts(ctx context.Context) error {
-	raw, source, err := b.client.fetch(ctx, "alerts", "/alerts/active", queryOptions{})
+	raw, source, err := b.client.fetch(ctx, "alerts", "/alerts/active", queryOptions{allowNull: true})
 	if err != nil {
 		return err
 	}
 	if raw == nil {
 		return b.handleMissing(&source, "active alerts data is missing", false)
 	}
+	if isJSONNull(raw) {
+		b.bundle.Alerts = &forecast.AlertRun{Raw: append(json.RawMessage(nil), raw...)}
+		b.addSource(source)
+		return nil
+	}
 	var alerts forecast.AlertRun
 	if err := decodeSource(raw, &alerts); err != nil {
 		return b.handleMalformed(&source, err, false)
@@ -301,6 +306,7 @@ func (c *Client) policyFor(source string) config.MissingSourcePolicy {
 type queryOptions struct {
 	precision bool
 	timezone  bool
+	allowNull bool
 }
 
 type envelope struct {
@@ -339,7 +345,7 @@ func (c *Client) fetch(ctx context.Context, sourceName string, endpoint string,
 		Query:     queryMap(reqURL.Query()),
 		FetchedAt: c.now(),
 	}
-	if len(env.Data) == 0 || bytes.Equal(bytes.TrimSpace(env.Data), []byte("null")) {
+	if len(env.Data) == 0 || (isJSONNull(env.Data) && !opts.allowNull) {
 		source.Missing = true
 		return nil, source, nil
 	}
@@ -351,6 +357,10 @@ func (c *Client) fetch(ctx context.Context, sourceName string, endpoint string,
 	return env.Data, source, nil
 }
 
+func isJSONNull(raw json.RawMessage) bool {
+	return bytes.Equal(bytes.TrimSpace(raw), []byte("null"))
+}
+
 func (c *Client) endpointURL(endpoint string, opts queryOptions) *url.URL {
 	reqURL := *c.baseURL
 	reqURL.Path = path.Join(c.baseURL.Path, endpoint)

internal/adapters/weatherapi/client_test.go

@@ -125,6 +125,36 @@ func TestRequiredHourlyForecast(t *testing.T) {
 	}
 }
 
+func TestNullAlertsMeansNoActiveAlerts(t *testing.T) {
+	server := fixtureServer(t, map[string]handlerOverride{
+		"/alerts/active": {status: http.StatusOK, body: `{"data": null}`},
+	}, nil)
+	client := newTestClient(t, server.URL+"/", nil)
+
+	bundle, err := client.FetchBundle(context.Background())
+	if err != nil {
+		t.Fatalf("FetchBundle() error = %v", err)
+	}
+	if bundle.Alerts == nil {
+		t.Fatal("Alerts = nil, want checked empty alert run")
+	}
+	if len(bundle.Alerts.Alerts) != 0 {
+		t.Fatalf("Alerts length = %d, want no active alerts", len(bundle.Alerts.Alerts))
+	}
+	source := sourceByName(t, bundle.Sources, "alerts")
+	if source.Missing {
+		t.Fatalf("alerts source Missing = true, want false")
+	}
+	if source.DataSHA256 == "" {
+		t.Fatal("alerts DataSHA256 is empty, want hash for explicit null payload")
+	}
+	for _, warning := range bundle.Warnings {
+		if warning.Source == "alerts" {
+			t.Fatalf("warnings = %#v, want no alerts warning", bundle.Warnings)
+		}
+	}
+}
+
 func TestMissingSourcePolicyWarnNoneError(t *testing.T) {
 	tests := []struct {
 		name       string