Improve handling of alerts when no active alerts are present

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