Fix a bug in the GeoJSON handling when there are no active polygons

internal/providers/spc/geojson.go

@@ -33,6 +33,11 @@ type GeoJSONProperties struct {
 	DN         *int   `json:"DN"`
 }
 
+type geometryMetadata struct {
+	Type       string            `json:"type"`
+	Geometries []json.RawMessage `json:"geometries"`
+}
+
 // DecodeGeoJSON decodes an SPC GeoJSON outlook product and compacts feature
 // geometry JSON for stable downstream storage.
 func DecodeGeoJSON(raw []byte) (GeoJSONFeatureCollection, error) {
@@ -50,6 +55,16 @@ func DecodeGeoJSON(raw []byte) (GeoJSONFeatureCollection, error) {
 	return collection, nil
 }
 
+// IsEmptyGeometryCollection reports whether raw is SPC's no-polygon placeholder
+// geometry shape: a GeometryCollection with no child geometries.
+func IsEmptyGeometryCollection(raw json.RawMessage) bool {
+	var meta geometryMetadata
+	if err := json.Unmarshal(raw, &meta); err != nil {
+		return false
+	}
+	return meta.Type == "GeometryCollection" && len(meta.Geometries) == 0
+}
+
 func (p *GeoJSONProperties) UnmarshalJSON(raw []byte) error {
 	type alias GeoJSONProperties
 	var aux struct {

internal/providers/spc/geojson_test.go

@@ -66,6 +66,43 @@ func TestDecodeGeoJSONParsesSeverityRankString(t *testing.T) {
 	}
 }
 
+func TestIsEmptyGeometryCollection(t *testing.T) {
+	tests := []struct {
+		name string
+		raw  string
+		want bool
+	}{
+		{
+			name: "empty geometry collection",
+			raw:  `{"type":"GeometryCollection","geometries":[]}`,
+			want: true,
+		},
+		{
+			name: "non-empty geometry collection",
+			raw:  `{"type":"GeometryCollection","geometries":[{"type":"Polygon","coordinates":[]} ]}`,
+			want: false,
+		},
+		{
+			name: "polygon",
+			raw:  `{"type":"Polygon","coordinates":[]}`,
+			want: false,
+		},
+		{
+			name: "invalid json",
+			raw:  `{`,
+			want: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := IsEmptyGeometryCollection([]byte(tt.raw)); got != tt.want {
+				t.Fatalf("IsEmptyGeometryCollection() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
 func TestParseISOTimestampTrimsAndReturnsUTC(t *testing.T) {
 	got, err := ParseISOTimestamp(" 2026-06-11T12:34:56Z ")
 	if err != nil {