Fix NPE in getObject(int, Class<T>) when column value is NULL (#1222) (#1227)

getObject(int, Class<T>) was missing a null guard before passing objects
to converters, causing NPE in DateConverter.toDate() and all other
converters when used by Spring DataClassRowMapper, Hibernate, etc. Added
null check in both DatabricksResultSet and ConverterHelper as
defense-in-depth, consistent with getObject(int) and getObject(int,
Map).

## Description
<!-- Provide a brief summary of the changes made and the issue they aim
to address.-->

## Testing
<!-- Describe how the changes have been tested-->
Added unit tests

## Additional Notes to the Reviewer
<!-- Share any additional context or insights that may help the reviewer
understand the changes better. This could include challenges faced,
limitations, or compromises made during the development process.
Also, mention any areas of the code that you would like the reviewer to
focus on specifically. -->

NO_CHANGELOG=true

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: gopalldb

src/main/java/com/databricks/jdbc/api/impl/DatabricksResultSet.java

@@ -1865,6 +1865,9 @@ public void updateNClob(String columnLabel, Reader reader) throws SQLException {
   public <T> T getObject(int columnIndex, Class<T> type) throws SQLException {
     checkIfClosed();
     Object obj = getObjectInternal(columnIndex);
+    if (obj == null) {
+      return null;
+    }
     int columnSqlType = resultSetMetaData.getColumnType(columnIndex);
     try {
       return (T) ConverterHelper.convertSqlTypeToSpecificJavaType(type, columnSqlType, obj);

src/main/java/com/databricks/jdbc/api/impl/converters/ConverterHelper.java

@@ -472,6 +472,9 @@ public static Object convertSqlTypeToJavaType(int columnSqlType, Object object)
    */
   public static Object convertSqlTypeToSpecificJavaType(
       Class<?> javaType, int columnSqlType, Object obj) throws DatabricksSQLException {
+    if (obj == null) {
+      return null;
+    }
     // Get the appropriate converter for the SQL type
     ObjectConverter converter = getConverterForSqlType(columnSqlType);
     if (javaType == String.class) {

src/test/java/com/databricks/jdbc/api/impl/DatabricksResultSetTest.java

@@ -1259,8 +1259,52 @@ void testIsComplexTypeThrowsExceptionWhenComplexDatatypeSupportIsDisabled() thro
         structException.getSQLState());
   }
 
-  // --- Tests for TelemetryCollector caching in next() ---
+  @Test
+  void testGetObjectWithClassType_NullDate_ReturnsNull() throws SQLException {
+    DatabricksResultSet resultSet = getResultSet(StatementState.SUCCEEDED, null);
+    when(mockedExecutionResult.getObject(0)).thenReturn(null);
+
+    assertNull(resultSet.getObject(1, Date.class));
+    assertTrue(resultSet.wasNull());
+  }
+
+  @Test
+  void testGetObjectWithClassType_NullTimestamp_ReturnsNull() throws SQLException {
+    DatabricksResultSet resultSet = getResultSet(StatementState.SUCCEEDED, null);
+    when(mockedExecutionResult.getObject(0)).thenReturn(null);
+
+    assertNull(resultSet.getObject(1, Timestamp.class));
+    assertTrue(resultSet.wasNull());
+  }
+
+  @Test
+  void testGetObjectWithClassType_NullLocalDate_ReturnsNull() throws SQLException {
+    DatabricksResultSet resultSet = getResultSet(StatementState.SUCCEEDED, null);
+    when(mockedExecutionResult.getObject(0)).thenReturn(null);
 
+    assertNull(resultSet.getObject(1, LocalDate.class));
+    assertTrue(resultSet.wasNull());
+  }
+
+  @Test
+  void testGetObjectWithClassType_NullInteger_ReturnsNull() throws SQLException {
+    DatabricksResultSet resultSet = getResultSet(StatementState.SUCCEEDED, null);
+    when(mockedExecutionResult.getObject(0)).thenReturn(null);
+
+    assertNull(resultSet.getObject(1, Integer.class));
+    assertTrue(resultSet.wasNull());
+  }
+
+  @Test
+  void testGetObjectWithClassType_NullString_ReturnsNull() throws SQLException {
+    DatabricksResultSet resultSet = getResultSet(StatementState.SUCCEEDED, null);
+    when(mockedExecutionResult.getObject(0)).thenReturn(null);
+
+    assertNull(resultSet.getObject(1, String.class));
+    assertTrue(resultSet.wasNull());
+  }
+  
+  // --- Tests for TelemetryCollector caching in next() ---
   private DatabricksResultSet getResultSetWithTelemetry() throws SQLException {
     DatabricksConnection mockConnection = mock(DatabricksConnection.class);
     IDatabricksConnectionContext mockContext = mock(IDatabricksConnectionContext.class);

src/test/java/com/databricks/jdbc/api/impl/converters/ConverterHelperTest.java

@@ -228,4 +228,19 @@ void whenColumnType_Other() {
     ObjectConverter converter = ConverterHelper.getConverterForSqlType(Types.DECIMAL);
     assertInstanceOf(BigDecimalConverter.class, converter);
   }
+
+  @Test
+  void testConvertSqlTypeToSpecificJavaType_NullObject_ReturnsNull() throws DatabricksSQLException {
+    assertNull(ConverterHelper.convertSqlTypeToSpecificJavaType(Date.class, Types.DATE, null));
+    assertNull(
+        ConverterHelper.convertSqlTypeToSpecificJavaType(Timestamp.class, Types.TIMESTAMP, null));
+    assertNull(ConverterHelper.convertSqlTypeToSpecificJavaType(LocalDate.class, Types.DATE, null));
+    assertNull(ConverterHelper.convertSqlTypeToSpecificJavaType(String.class, Types.VARCHAR, null));
+    assertNull(
+        ConverterHelper.convertSqlTypeToSpecificJavaType(Integer.class, Types.INTEGER, null));
+    assertNull(ConverterHelper.convertSqlTypeToSpecificJavaType(Long.class, Types.BIGINT, null));
+    assertNull(ConverterHelper.convertSqlTypeToSpecificJavaType(Double.class, Types.DOUBLE, null));
+    assertNull(
+        ConverterHelper.convertSqlTypeToSpecificJavaType(BigDecimal.class, Types.DECIMAL, null));
+  }
 }