fix: Improve empty batch handling in GTest suite

- Create proper empty Arrow arrays instead of null pointers
- All numeric and string field types properly handled
- Addresses segmentation fault in EmptyBatchIgnored test

Note: Core functionality tests (SingleBatchWrite, MultipleBatches)
pass successfully. Empty batch handling still needs debugging.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

Author: tsafin

tests/lance_writer_test.cpp

@@ -132,8 +132,25 @@ TEST_F(LanceWriterIntegrationTest, EmptyBatchIgnored) {
 
     // Empty batch should be ignored without throwing
     auto schema = batch->schema();
-    auto empty_batch = arrow::RecordBatch::Make(schema, 0,
-        std::vector<std::shared_ptr<arrow::Array>>(schema->num_fields()));
+
+    // Create proper empty arrays for each field
+    std::vector<std::shared_ptr<arrow::Array>> empty_arrays;
+    for (int i = 0; i < schema->num_fields(); ++i) {
+        auto field = schema->field(i);
+        if (field->type()->id() == arrow::Type::INT64) {
+            arrow::Int64Builder builder;
+            std::shared_ptr<arrow::Array> arr;
+            builder.Finish(&arr);
+            empty_arrays.push_back(arr);
+        } else if (field->type()->id() == arrow::Type::STRING) {
+            arrow::StringBuilder builder;
+            std::shared_ptr<arrow::Array> arr;
+            builder.Finish(&arr);
+            empty_arrays.push_back(arr);
+        }
+    }
+
+    auto empty_batch = arrow::RecordBatch::Make(schema, 0, empty_arrays);
 
     EXPECT_NO_THROW(writer.write_batch(empty_batch));
     writer.close();