fix(bigquery-jdbc): avoid NPE for null values in Storage Write API batch insert

java-bigquery-jdbc/pom.xml

@@ -456,6 +456,20 @@
       <version>2.96.0-SNAPSHOT</version><!-- {x-version-update:google-cloud-trace:current} -->
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>com.google.cloud</groupId>
+      <artifactId>google-cloud-bigquerystorage</artifactId>
+      <version>3.32.0-SNAPSHOT</version><!-- {x-version-update:google-cloud-bigquerystorage:current} -->
+      <classifier>tests</classifier>
+      <type>test-jar</type>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>com.google.api</groupId>
+      <artifactId>gax-grpc</artifactId>
+      <classifier>testlib</classifier>
+      <scope>test</scope>
+    </dependency>
   </dependencies>
 
   <profiles>

java-bigquery-jdbc/src/main/java/com/google/cloud/bigquery/jdbc/BigQueryPreparedStatement.java

@@ -34,6 +34,7 @@
 import com.google.cloud.bigquery.storage.v1.TableName;
 import com.google.gson.Gson;
 import com.google.gson.JsonArray;
+import com.google.gson.JsonNull;
 import com.google.gson.JsonObject;
 import com.google.protobuf.Descriptors.DescriptorValidationException;
 import java.io.IOException;
@@ -392,7 +393,9 @@ private long bulkInsertWithWriteAPI(BigQueryWriteClient bigQueryWriteClient)
           JsonObject rowObject = new JsonObject();
           for (int j = 0; j < parameterList.size(); j++) {
             BigQueryJdbcParameter parameter = parameterList.get(j);
-            if (parameter.getSqlType() == StandardSQLTypeName.STRING) {
+            if (parameter.getValue() == null) {
+              rowObject.add(fieldLists.get(j).getName(), JsonNull.INSTANCE);
+            } else if (parameter.getSqlType() == StandardSQLTypeName.STRING) {
               rowObject.addProperty(fieldLists.get(j).getName(), parameter.getValue().toString());
             } else {
               rowObject.addProperty(fieldLists.get(j).getName(), gson.toJson(parameter.getValue()));

java-bigquery-jdbc/src/test/java/com/google/cloud/bigquery/jdbc/BigQueryPreparedStatementBulkInsertNullValueTest.java

@@ -0,0 +1,138 @@
+/*
+ * Copyright 2026 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.cloud.bigquery.jdbc;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.mockito.Mockito.mock;
+
+import com.google.api.gax.core.NoCredentialsProvider;
+import com.google.api.gax.grpc.testing.LocalChannelProvider;
+import com.google.api.gax.grpc.testing.MockGrpcService;
+import com.google.api.gax.grpc.testing.MockServiceHelper;
+import com.google.cloud.bigquery.Field;
+import com.google.cloud.bigquery.Schema;
+import com.google.cloud.bigquery.StandardSQLTypeName;
+import com.google.cloud.bigquery.storage.v1.AppendRowsResponse;
+import com.google.cloud.bigquery.storage.v1.BatchCommitWriteStreamsResponse;
+import com.google.cloud.bigquery.storage.v1.BigQueryWriteClient;
+import com.google.cloud.bigquery.storage.v1.BigQueryWriteSettings;
+import com.google.cloud.bigquery.storage.v1.FinalizeWriteStreamResponse;
+import com.google.cloud.bigquery.storage.v1.MockBigQueryWrite;
+import com.google.cloud.bigquery.storage.v1.TableFieldSchema;
+import com.google.cloud.bigquery.storage.v1.TableName;
+import com.google.cloud.bigquery.storage.v1.TableSchema;
+import com.google.cloud.bigquery.storage.v1.WriteStream;
+import com.google.protobuf.Int64Value;
+import com.google.protobuf.Timestamp;
+import java.lang.reflect.Method;
+import java.sql.Types;
+import java.util.Arrays;
+import java.util.UUID;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Regression test for https://github.com/googleapis/google-cloud-java/issues/14066: a
+ * null-valued STRING parameter in a Storage Write API batch insert used to throw NPE while
+ * building the row's JSON representation, instead of writing a JSON null. Drives the real
+ * bulkInsertWithWriteAPI code path end-to-end against an in-process fake Storage Write service so
+ * the fix is verified without any real network dependency.
+ */
+public class BigQueryPreparedStatementBulkInsertNullValueTest {
+
+  private static final String STREAM_NAME =
+      "projects/test-project/datasets/test_dataset/tables/test_table/streams/test-stream";
+
+  private MockBigQueryWrite mockBigQueryWrite;
+  private MockServiceHelper serviceHelper;
+  private BigQueryWriteClient writeClient;
+  private BigQueryPreparedStatement preparedStatement;
+
+  @BeforeEach
+  public void setUp() throws Exception {
+    mockBigQueryWrite = new MockBigQueryWrite();
+    serviceHelper =
+        new MockServiceHelper(
+            UUID.randomUUID().toString(), Arrays.<MockGrpcService>asList(mockBigQueryWrite));
+    serviceHelper.start();
+
+    LocalChannelProvider channelProvider = serviceHelper.createChannelProvider();
+    writeClient =
+        BigQueryWriteClient.create(
+            BigQueryWriteSettings.newBuilder()
+                .setTransportChannelProvider(channelProvider)
+                .setCredentialsProvider(NoCredentialsProvider.create())
+                .build());
+
+    TableFieldSchema nameField =
+        TableFieldSchema.newBuilder()
+            .setName("name")
+            .setType(TableFieldSchema.Type.STRING)
+            .setMode(TableFieldSchema.Mode.NULLABLE)
+            .build();
+    WriteStream writeStream =
+        WriteStream.newBuilder()
+            .setName(STREAM_NAME)
+            .setTableSchema(TableSchema.newBuilder().addFields(nameField).build())
+            .build();
+
+    // Responses are consumed in call order by bulkInsertWithWriteAPI: createWriteStream, then
+    // append, then finalizeWriteStream, then batchCommitWriteStreams.
+    mockBigQueryWrite.addResponse(writeStream);
+    mockBigQueryWrite.addResponse(
+        AppendRowsResponse.newBuilder()
+            .setAppendResult(
+                AppendRowsResponse.AppendResult.newBuilder().setOffset(Int64Value.of(0)))
+            .build());
+    mockBigQueryWrite.addResponse(FinalizeWriteStreamResponse.newBuilder().setRowCount(1).build());
+    mockBigQueryWrite.addResponse(
+        BatchCommitWriteStreamsResponse.newBuilder()
+            .setCommitTime(Timestamp.newBuilder().build())
+            .build());
+
+    BigQueryConnection connection = mock(BigQueryConnection.class);
+    preparedStatement =
+        new BigQueryPreparedStatement(connection, "INSERT INTO test_table (name) VALUES (?)");
+    preparedStatement.insertSchema = Schema.of(Field.of("name", StandardSQLTypeName.STRING));
+
+    java.lang.reflect.Field insertTableNameField =
+        BigQueryPreparedStatement.class.getDeclaredField("insertTableName");
+    insertTableNameField.setAccessible(true);
+    insertTableNameField.set(
+        preparedStatement, TableName.of("test-project", "test_dataset", "test_table"));
+  }
+
+  @AfterEach
+  public void tearDown() throws Exception {
+    writeClient.close();
+    serviceHelper.stop();
+  }
+
+  @Test
+  public void testBulkInsertWithWriteApiCompletesForNullStringParameter() throws Exception {
+    preparedStatement.setNull(1, Types.VARCHAR);
+    preparedStatement.addBatch();
+
+    Method bulkInsertMethod =
+        BigQueryPreparedStatement.class.getDeclaredMethod(
+            "bulkInsertWithWriteAPI", BigQueryWriteClient.class);
+    bulkInsertMethod.setAccessible(true);
+
+    assertDoesNotThrow(() -> bulkInsertMethod.invoke(preparedStatement, writeClient));
+  }
+}