[GitHub] [calcite] rubenada commented on a change in pull request #2353: [CALCITE-2000] UNNEST a collection that has a field with nested data generates an Exception

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rubenada commented on a change in pull request #2353:
URL: https://github.com/apache/calcite/pull/2353#discussion_r583635078



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File path: core/src/main/java/org/apache/calcite/runtime/SqlFunctions.java
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@@ -2792,27 +2792,28 @@ public static Collection multisetUnionAll(Collection collection1,
    * Function that, given a certain List containing single-item structs (i.e. arrays / lists with
    * a single item), builds an Enumerable that returns those single items inside the structs.
    */
-  public static Function1<Object, Enumerable<Comparable>> flatList() {
+  public static Function1<Object, Enumerable<Object>> flatList() {

Review comment:
       {{SqlFunction#flatList}} was introduced in 1.24 via CALCITE-4063, and it is a counter-part of {{flatProduct}} for a very particular case. So, following {{flatProduct}}'s logic, inputObject cannot be null, so I guess {{flatList}} should look like:
   ```
     public static Function1<Object, Enumerable<Object>> flatList() {
       return inputObject -> {
         //noinspection unchecked
         final List<Object> list = (List<Object>) inputObject;
         final Enumerator<Object> enumerator = Linq4j.enumerator(list);
         ...
   ```
   do you agree?      




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