fix: dry run NPE when there is no query parameters (#2899)

Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:
- [X] Make sure to open an issue as a [bug/issue](https://togithub.com/googleapis/java-bigquery/issues/new/choose) before writing your code!  That way we can discuss the change, evaluate designs, and agree on the general idea
- [X] Ensure the tests and linter pass
- [X] Code coverage does not decrease (if any source code was changed)
- [X] Appropriate docs were updated (if necessary)

Fixes #2895 ☕️

Author: obada-ab

google-cloud-bigquery/src/main/java/com/google/cloud/bigquery/ConnectionImpl.java

@@ -55,6 +55,7 @@
 import java.io.IOException;
 import java.util.AbstractList;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.LinkedList;
 import java.util.List;
@@ -173,7 +174,9 @@ public BigQueryDryRunResult dryRun(String sql) throws BigQuerySQLException {
     List<QueryParameter> queryParametersPb =
         dryRunJob.getStatistics().getQuery().getUndeclaredQueryParameters();
     List<Parameter> queryParameters =
-        Lists.transform(queryParametersPb, QUERY_PARAMETER_FROM_PB_FUNCTION);
+        queryParametersPb == null
+            ? Collections.emptyList()
+            : Lists.transform(queryParametersPb, QUERY_PARAMETER_FROM_PB_FUNCTION);
     QueryStatistics queryStatistics = JobStatistics.fromPb(dryRunJob);
     SessionInfo sessionInfo =
         queryStatistics.getSessionInfo() == null ? null : queryStatistics.getSessionInfo();

google-cloud-bigquery/src/test/java/com/google/cloud/bigquery/ConnectionImplTest.java

@@ -237,6 +237,34 @@ public void testQueryDryRun() throws BigQuerySQLException {
         .createJobForQuery(any(com.google.api.services.bigquery.model.Job.class));
   }
 
+  @Test
+  public void testQueryDryRunNoQueryParameters() throws BigQuerySQLException {
+    com.google.api.services.bigquery.model.JobStatistics2 queryMock =
+        new com.google.api.services.bigquery.model.JobStatistics2()
+            .setSchema(FAST_QUERY_TABLESCHEMA);
+    com.google.api.services.bigquery.model.JobStatistics jobStatsMock =
+        new com.google.api.services.bigquery.model.JobStatistics()
+            .setCreationTime(1234L)
+            .setStartTime(5678L)
+            .setQuery(queryMock);
+    com.google.api.services.bigquery.model.JobConfigurationQuery jobConfigurationQuery =
+        new com.google.api.services.bigquery.model.JobConfigurationQuery();
+    com.google.api.services.bigquery.model.JobConfiguration jobConfig =
+        new com.google.api.services.bigquery.model.JobConfiguration()
+            .setQuery(jobConfigurationQuery);
+    com.google.api.services.bigquery.model.Job mockDryRunJob =
+        new com.google.api.services.bigquery.model.Job()
+            .setStatistics(jobStatsMock)
+            .setConfiguration(jobConfig);
+    when(bigqueryRpcMock.createJobForQuery(any(com.google.api.services.bigquery.model.Job.class)))
+        .thenReturn(mockDryRunJob);
+    BigQueryDryRunResult dryRunResult = connection.dryRun(DRY_RUN_SQL);
+    assertEquals(0, dryRunResult.getQueryParameters().size());
+    assertEquals(QUERY_SCHEMA, dryRunResult.getSchema());
+    verify(bigqueryRpcMock, times(1))
+        .createJobForQuery(any(com.google.api.services.bigquery.model.Job.class));
+  }
+
   @Test
   public void testParseDataTask() throws InterruptedException {
     BlockingQueue<Tuple<Iterable<FieldValueList>, Boolean>> pageCache =

google-cloud-bigquery/src/test/java/com/google/cloud/bigquery/it/ITBigQueryTest.java

@@ -2989,6 +2989,34 @@ public void testConnectionImplDryRun() throws SQLException {
     assertEquals(StatementType.SELECT, queryStatistics.getStatementType());
   }
 
+  @Test
+  public void testConnectionImplDryRunNoQueryParameters() throws SQLException {
+    String query =
+        String.format(
+            "select StringField,  BigNumericField, BooleanField, BytesField, IntegerField, "
+                + "TimestampField, FloatField, NumericField, TimeField, DateField,  DateTimeField, "
+                + "GeographyField, RecordField.BytesField, RecordField.BooleanField, "
+                + "IntegerArrayField from %s order by TimestampField",
+            TABLE_ID_FASTQUERY_BQ_RESULTSET.getTable());
+    ConnectionSettings connectionSettings =
+        ConnectionSettings.newBuilder()
+            .setDefaultDataset(DatasetId.of(DATASET))
+            .setCreateSession(true)
+            .build();
+    Connection connection = bigquery.createConnection(connectionSettings);
+    BigQueryDryRunResult bigQueryDryRunResultSet = connection.dryRun(query);
+    assertNotNull(bigQueryDryRunResultSet.getSchema());
+    assertEquals(
+        BQ_RESULTSET_EXPECTED_SCHEMA, bigQueryDryRunResultSet.getSchema()); // match the schema
+    List<Parameter> queryParameters = bigQueryDryRunResultSet.getQueryParameters();
+    assertEquals(0, queryParameters.size());
+    QueryStatistics queryStatistics = bigQueryDryRunResultSet.getStatistics().getQueryStatistics();
+    assertNotNull(queryStatistics);
+    SessionInfo sessionInfo = bigQueryDryRunResultSet.getStatistics().getSessionInfo();
+    assertNotNull(sessionInfo.getSessionId());
+    assertEquals(StatementType.SELECT, queryStatistics.getStatementType());
+  }
+
   @Test
   // This test case test the order of the records, making sure that the result is not jumbled up due
   // to the multithreaded BigQueryResult implementation