[GitHub] [iceberg] stevenzwu commented on a diff in pull request #7517: API, Flink: StructProjection returns null projection object for null nested struct value

["stevenzwu (via GitHub)" <gi...@apache.org>]

stevenzwu commented on code in PR #7517:
URL: https://github.com/apache/iceberg/pull/7517#discussion_r1185469804


##########
api/src/main/java/org/apache/iceberg/util/StructProjection.java:
##########
@@ -189,16 +189,12 @@ public int size() {
 
   @Override
   public <T> T get(int pos, Class<T> javaClass) {
-    if (struct == null) {
-      // Return a null struct when projecting a nested required field from an optional struct.
-      // See more details in issue #2738.
-      return null;
-    }
-
     int structPos = positionMap[pos];
-
     if (nestedProjections[pos] != null) {
-      return javaClass.cast(nestedProjections[pos].wrap(struct.get(structPos, StructLike.class)));
+      StructLike nestedStruct = struct.get(structPos, StructLike.class);

Review Comment:
   good question. this change avoided the wrapping null at nested level, [which is the main reason we added the lines from 192-196](https://github.com/apache/iceberg/issues/2738) that are removed in this PR. 
   
   I guess it can potentially happen if we use `StructProjection` to wrap a null `struct` at the root level. If it is a valid scenario, we need to bring back line 192-196. If it is not a valid scenario, we should add `Preconditions` check in the wrap method.
   ```
     public StructProjection wrap(StructLike newStruct) {
       this.struct = newStruct;
       return this;
     }
   ```
   
   My take is that StructProjection shouldn't wrap a null root value.



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