when aliasing to null, use alias'es id for subsequent aliases

Author: bpintea

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/optimizer/rules/RuleUtils.java

@@ -30,9 +30,11 @@ public final class RuleUtils {
     private RuleUtils() {}
 
     /**
-     * Returns a tuple of two lists:
-     * 1. A list of aliases to null literals for those data types in the {@param outputAttributes} that {@param shouldBeReplaced}.
-     * 2. A list of named expressions where attributes that match the predicate are replaced with their corresponding null alias.
+     * @return a tuple of two lists:
+     * <ol>
+     * <li>A list of aliases to null literals for those data types in the {@code outputAttributes} that {@code shouldBeReplaced}.</li>
+     * <li>A list of named expressions where attributes that match the predicate are replaced with their corresponding null alias.</li>
+     * </ol>
      *
      * @param outputAttributes The original output attributes.
      * @param shouldBeReplaced A predicate to determine which attributes should be replaced with null aliases.
@@ -63,7 +65,7 @@ public static Tuple<List<Alias>, List<NamedExpression>> aliasedNulls(
                 }
                 // otherwise point to it since this avoids creating field copies
                 else {
-                    projection = new Alias(attr.source(), attr.name(), nullAlias.toAttribute(), attr.id());
+                    projection = new Alias(attr.source(), attr.name(), nullAlias.toAttribute(), nullAlias.id());
                 }
             } else {
                 projection = attr;