[minor] following 3304, some code refactoring (apache#6713)

Author: danny0405

hudi-client/hudi-client-common/src/main/java/org/apache/hudi/execution/HoodieLazyInsertIterable.java

@@ -105,7 +105,7 @@ static <T extends HoodieRecordPayload> Function<HoodieRecord<T>, HoodieInsertVal
 
   static <T extends HoodieRecordPayload> Function<HoodieRecord<T>, HoodieInsertValueGenResult<HoodieRecord>> getTransformFunction(
       Schema schema) {
-    return hoodieRecord -> new HoodieInsertValueGenResult(hoodieRecord, schema, CollectionUtils.EMPTY_PROPERTIES);
+    return hoodieRecord -> new HoodieInsertValueGenResult(hoodieRecord, schema, CollectionUtils.emptyProps());
   }
 
   @Override

hudi-client/hudi-client-common/src/main/java/org/apache/hudi/table/action/commit/HoodieWriteHelper.java

@@ -26,12 +26,11 @@
 import org.apache.hudi.common.model.HoodieKey;
 import org.apache.hudi.common.model.HoodieRecord;
 import org.apache.hudi.common.model.HoodieRecordPayload;
+import org.apache.hudi.common.util.CollectionUtils;
 import org.apache.hudi.common.util.collection.Pair;
 import org.apache.hudi.index.HoodieIndex;
 import org.apache.hudi.table.HoodieTable;
 
-import java.util.Properties;
-
 public class HoodieWriteHelper<T extends HoodieRecordPayload, R> extends BaseWriteHelper<T, HoodieData<HoodieRecord<T>>,
     HoodieData<HoodieKey>, HoodieData<WriteStatus>, R> {
 
@@ -64,7 +63,7 @@ public HoodieData<HoodieRecord<T>> deduplicateRecords(
       return Pair.of(key, record);
     }).reduceByKey((rec1, rec2) -> {
       @SuppressWarnings("unchecked")
-      T reducedData = (T) rec2.getData().preCombine(rec1.getData(), schema.get(), new Properties());
+      T reducedData = (T) rec2.getData().preCombine(rec1.getData(), schema.get(), CollectionUtils.emptyProps());
       HoodieKey reducedKey = rec1.getData().equals(reducedData) ? rec1.getKey() : rec2.getKey();
 
       return new HoodieAvroRecord<>(reducedKey, reducedData);

hudi-client/hudi-flink-client/src/main/java/org/apache/hudi/table/action/commit/FlinkWriteHelper.java

@@ -27,6 +27,7 @@
 import org.apache.hudi.common.model.HoodieRecord;
 import org.apache.hudi.common.model.HoodieRecordPayload;
 import org.apache.hudi.common.model.WriteOperationType;
+import org.apache.hudi.common.util.CollectionUtils;
 import org.apache.hudi.exception.HoodieUpsertException;
 import org.apache.hudi.index.HoodieIndex;
 import org.apache.hudi.table.HoodieTable;
@@ -39,7 +40,6 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
-import java.util.Properties;
 import java.util.stream.Collectors;
 
 /**
@@ -102,7 +102,7 @@ public List<HoodieRecord<T>> deduplicateRecords(
       final T data1 = rec1.getData();
       final T data2 = rec2.getData();
 
-      @SuppressWarnings("unchecked") final T reducedData = (T) data2.preCombine(data1, schema, new Properties());
+      @SuppressWarnings("unchecked") final T reducedData = (T) data2.preCombine(data1, schema, CollectionUtils.emptyProps());
       // we cannot allow the user to change the key or partitionPath, since that will affect
       // everything
       // so pick it from one of the records.

hudi-client/hudi-java-client/src/main/java/org/apache/hudi/table/action/commit/JavaWriteHelper.java

@@ -25,6 +25,7 @@
 import org.apache.hudi.common.model.HoodieKey;
 import org.apache.hudi.common.model.HoodieRecord;
 import org.apache.hudi.common.model.HoodieRecordPayload;
+import org.apache.hudi.common.util.CollectionUtils;
 import org.apache.hudi.common.util.collection.Pair;
 import org.apache.hudi.index.HoodieIndex;
 import org.apache.hudi.table.HoodieTable;
@@ -34,7 +35,6 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
-import java.util.Properties;
 import java.util.stream.Collectors;
 
 public class JavaWriteHelper<T extends HoodieRecordPayload,R> extends BaseWriteHelper<T, List<HoodieRecord<T>>,
@@ -70,7 +70,7 @@ public List<HoodieRecord<T>> deduplicateRecords(
     final Schema schema = new Schema.Parser().parse(schemaStr);
     return keyedRecords.values().stream().map(x -> x.stream().map(Pair::getRight).reduce((rec1, rec2) -> {
       @SuppressWarnings("unchecked")
-      T reducedData = (T) rec1.getData().preCombine(rec2.getData(), schema, new Properties());
+      T reducedData = (T) rec1.getData().preCombine(rec2.getData(), schema, CollectionUtils.emptyProps());
       // we cannot allow the user to change the key or partitionPath, since that will affect
       // everything
       // so pick it from one of the records.

hudi-common/src/main/java/org/apache/hudi/common/util/CollectionUtils.java

@@ -44,7 +44,15 @@
 
 public class CollectionUtils {
 
-  public static final Properties EMPTY_PROPERTIES = new Properties();
+  private static final Properties EMPTY_PROPERTIES = new Properties();
+
+  /**
+   * Returns an empty {@code Properties} instance. The props instance is a singleton,
+   * it should not be modified in any case.
+   */
+  public static Properties emptyProps() {
+    return EMPTY_PROPERTIES;
+  }
 
   public static boolean isNullOrEmpty(Collection<?> c) {
     return Objects.isNull(c) || c.isEmpty();