change the behavior of merge null or invalid statistics

Tested the following cases after the changes:
- Merging valid stats with null stats results in invalid stats with null components
- Merging null stats with valid stats also results in invalid stats with null components
- Merging valid stats with partially null stats (null bounding box) results in the expected behavior where only the bounding box becomes null

Author: zhangfengcdt

parquet-column/src/main/java/org/apache/parquet/column/statistics/geometry/BoundingBox.java

@@ -150,15 +150,14 @@ public boolean isEmpty() {
    * @param other the other BoundingBox whose bounds will be merged into this one
    */
   public void merge(BoundingBox other) {
-    // Skip merging if the bbox is not valid or other is null or empty
-    // - A null bounding box cannot be merged
-    // - An empty bounding box (with inverted min/max) has no effect when merged,
-    //   so we can skip the merge operation entirely for efficiency
     if (!valid) {
       return;
     }
 
-    if (other == null || other.isEmpty()) {
+    // If other is null or invalid, mark this as invalid
+    if (other == null || other.isEmpty() || !other.valid) {
+      valid = false;
+      resetBBox();
       return;
     }
 
@@ -184,7 +183,6 @@ public void merge(BoundingBox other) {
    *                If null or empty, the method returns without making any changes.
    */
   public void update(Geometry geometry) {
-    // Skip updating if the bbox is not valid or geometry is null or empty
     if (!valid) {
       return;
     }

parquet-column/src/main/java/org/apache/parquet/column/statistics/geometry/GeospatialStatistics.java

@@ -37,9 +37,9 @@ public class GeospatialStatistics {
   private static final Logger LOG = LoggerFactory.getLogger(GeospatialStatistics.class);
 
   // Metadata that may impact the statistics calculation
-  private final BoundingBox boundingBox;
   private final EdgeInterpolationAlgorithm edgeAlgorithm;
-  private final GeospatialTypes geospatialTypes;
+  private BoundingBox boundingBox;
+  private GeospatialTypes geospatialTypes;
 
   /**
    * Merge the statistics from another GeospatialStatistics object.
@@ -196,11 +196,21 @@ public boolean isValid() {
   public void merge(GeospatialStatistics other) {
     Preconditions.checkArgument(other != null, "Cannot merge with null GeometryStatistics");
 
-    if (boundingBox != null && other.boundingBox != null) {
+    // If other bounding box is null or invalid, set this as null
+    if (boundingBox == null || other.boundingBox == null) {
+      boundingBox = null;
+    }
+
+    if (boundingBox != null) {
       boundingBox.merge(other.boundingBox);
     }
 
-    if (geospatialTypes != null && other.geospatialTypes != null) {
+    // If other geosptialTypes is null or invalid, set this as null
+    if (geospatialTypes == null || other.geospatialTypes == null) {
+      geospatialTypes = null;
+    }
+
+    if (geospatialTypes != null) {
       geospatialTypes.merge(other.geospatialTypes);
     }
   }

parquet-column/src/main/java/org/apache/parquet/column/statistics/geometry/GeospatialTypes.java

@@ -21,7 +21,6 @@
 import java.util.HashSet;
 import java.util.Set;
 import java.util.stream.Collectors;
-import org.apache.parquet.Preconditions;
 import org.locationtech.jts.geom.Coordinate;
 import org.locationtech.jts.geom.Geometry;
 
@@ -45,6 +44,11 @@ void update(Geometry geometry) {
     if (!valid) {
       return;
     }
+
+    if (geometry == null || geometry.isEmpty()) {
+      return;
+    }
+
     int code = getGeometryTypeCode(geometry);
     if (code != UNKNOWN_TYPE_ID) {
       types.add(code);
@@ -55,11 +59,12 @@ void update(Geometry geometry) {
   }
 
   public void merge(GeospatialTypes other) {
-    Preconditions.checkArgument(other != null, "Cannot merge with null GeospatialTypes");
     if (!valid) {
       return;
     }
-    if (!other.valid) {
+
+    // If other is null or invalid, mark this as invalid
+    if (other == null || !other.valid) {
       valid = false;
       types.clear();
       return;

parquet-column/src/test/java/org/apache/parquet/column/statistics/geometry/TestGeospatialStatistics.java

@@ -71,6 +71,55 @@ public void testMergeGeospatialStatistics() throws ParseException {
     Assert.assertNotNull(statistics1.getGeospatialTypes());
   }
 
+  @Test
+  public void testMergeNullGeospatialStatistics() {
+    // Create a valid stats object
+    PrimitiveType type = Types.optional(PrimitiveType.PrimitiveTypeName.BINARY)
+        .as(LogicalTypeAnnotation.geometryType(null))
+        .named("a");
+
+    WKTReader wktReader = new WKTReader();
+    WKBWriter wkbWriter = new WKBWriter();
+
+    GeospatialStatistics.Builder validBuilder = GeospatialStatistics.newBuilder(type);
+    try {
+      validBuilder.update(Binary.fromConstantByteArray(wkbWriter.write(wktReader.read("POINT (1 1)"))));
+    } catch (ParseException e) {
+      Assert.fail("Failed to parse valid WKT: " + e.getMessage());
+    }
+    GeospatialStatistics validStats = validBuilder.build();
+    Assert.assertTrue(validStats.isValid());
+
+    // Create stats with null components
+    GeospatialStatistics nullStats = new GeospatialStatistics(null, null, null);
+    Assert.assertFalse(nullStats.isValid());
+
+    // Test merging valid with null
+    GeospatialStatistics validCopy = validStats.copy();
+    validCopy.merge(nullStats);
+    Assert.assertFalse(validCopy.isValid());
+    Assert.assertNull(validCopy.getBoundingBox());
+    Assert.assertNull(validCopy.getGeospatialTypes());
+
+    // Test merging null with valid
+    nullStats = new GeospatialStatistics(null, null, null);
+    nullStats.merge(validStats);
+    Assert.assertFalse(nullStats.isValid());
+    Assert.assertNull(nullStats.getBoundingBox());
+    Assert.assertNull(nullStats.getGeospatialTypes());
+
+    // Create stats with null bounding box only
+    GeospatialStatistics nullBboxStats = new GeospatialStatistics(null, new GeospatialTypes(), null);
+    Assert.assertFalse(nullBboxStats.isValid());
+
+    // Test merging valid with null bounding box
+    validCopy = validStats.copy();
+    validCopy.merge(nullBboxStats);
+    Assert.assertFalse(validCopy.isValid());
+    Assert.assertNull(validCopy.getBoundingBox());
+    Assert.assertNotNull(validCopy.getGeospatialTypes());
+  }
+
   @Test
   public void testCopyGeospatialStatistics() {
     PrimitiveType type = Types.optional(PrimitiveType.PrimitiveTypeName.BINARY)