fix: the npe of ReorderableStruct reorder method

Author: dingxin-tech

odps-sdk/odps-sdk-core/src/main/java/com/aliyun/odps/data/ReorderableStruct.java

@@ -119,6 +119,9 @@ public synchronized void reorder(StructTypeInfo orderedType) {
   }
 
   public static Object reorderNestedType(Object value, TypeInfo oldTypeInfo, TypeInfo newTypeInfo) {
+    if (value == null) {
+      return null;
+    }
     if (oldTypeInfo != null && oldTypeInfo.getOdpsType() != newTypeInfo.getOdpsType()) {
       throw new IllegalArgumentException("The nested type is not compatible");
     }