diff --git a/src/backend/optimizer/path/uniquekeys.c b/src/backend/optimizer/path/uniquekeys.c
index 91be8a7f6ec..19c894bbea7 100644
--- a/src/backend/optimizer/path/uniquekeys.c
+++ b/src/backend/optimizer/path/uniquekeys.c
@@ -179,9 +179,17 @@ populate_plain_rel_uniquekeys(PlannerInfo *root, RelOptInfo *rel)
 					nonnullable_valid = true;
 				}
 
+				/*
+				 * NULLs in this column do not disambiguate the output rows,
+				 * so the output rows will only be truly distinct if the rows
+				 * containing NULL in this column will be filtered out
+				 * altogether.
+				 */
 				if (!IsA(colexpr, Var) ||
-					(!var_is_nonnullable(root, (Var *) colexpr, NOTNULL_SOURCE_RELOPT) &&
-					 !var_in_nonnullable_vars((Var *) colexpr, nonnullable_vars)))
+					(!var_is_nonnullable(root, castNode(Var, colexpr),
+										 NOTNULL_SOURCE_RELOPT) &&
+					 !var_in_nonnullable_vars(castNode(Var, colexpr),
+											  nonnullable_vars)))
 					nullable = true;
 			}
 		}
@@ -246,7 +254,7 @@ populate_subquery_rel_uniquekeys(PlannerInfo *root, RelOptInfo *rel)
 				continue;
 
 			Assert(lg != NULL);
-			sgc = (SortGroupClause *) lfirst(lg);
+			sgc = lfirst_node(SortGroupClause, lg);
 			lg = lnext(topop->groupClauses, lg);
 
 			if (!add_subquery_key_col(root, rel, sgc, tle, &key_ecs))
@@ -484,9 +492,9 @@ populate_joinrel_uniquekeys(PlannerInfo *root, RelOptInfo *joinrel,
 
 	/*
 	 * Preservation of the LHS keys: unconditional for a semi/antijoin, else
-	 * the RHS must be unique for the clauses so each LHS row yields one join
-	 * row.  A lateral reference into the RHS re-executes the LHS per RHS row,
-	 * voiding this.
+	 * the RHS must be unique for the clauses so each LHS row yields at most
+	 * one join row.  A lateral reference into the RHS re-executes the LHS per
+	 * RHS row, voiding this.
 	 */
 	if (lhs->uniquekeys != NIL &&
 		!bms_overlap(lhs->lateral_relids, rhs->relids) &&
@@ -853,7 +861,7 @@ uniquekeys_grouping_is_noop(PlannerInfo *root, RelOptInfo *input_rel)
 		if (foreach_current_index(lc) >= root->num_groupby_pathkeys)
 			break;
 
-		pos = base_ec_position(root, ((PathKey *) lfirst(lc))->pk_eclass);
+		pos = base_ec_position(root, castNode(PathKey, lfirst(lc))->pk_eclass);
 		if (pos >= 0)
 			covered = bms_add_member(covered, pos);
 	}
@@ -1018,7 +1026,7 @@ get_interesting_unique_ecs(PlannerInfo *root)
 				break;
 
 			result = add_base_ec_positions(root, result,
-										   ((PathKey *) lfirst(lc))->pk_eclass);
+										   castNode(PathKey, lc)->pk_eclass);
 		}
 	}
 
@@ -1138,7 +1146,7 @@ collect_clause_ecs(PlannerInfo *root, List *clause, Bitmapset **ecs_p)
 		}
 		if (pos < 0)
 			return false;
-		ec = (EquivalenceClass *) list_nth(root->eq_classes, pos);
+		ec = list_nth_node(EquivalenceClass, root->eq_classes, pos);
 
 		if (!ec->ec_has_const)
 			ecs = bms_add_member(ecs, pos);
@@ -1191,12 +1199,8 @@ add_uniquekey(RelOptInfo *rel, Bitmapset *eclass_indexes, bool nullable)
 static bool
 rel_has_uniquekey_within(RelOptInfo *rel, Bitmapset *ecs, bool null_aware)
 {
-	ListCell   *lc;
-
-	foreach(lc, rel->uniquekeys)
+	foreach_node(UniqueKey, ukey, rel->uniquekeys)
 	{
-		UniqueKey  *ukey = lfirst_node(UniqueKey, lc);
-
 		if ((!null_aware || !ukey->nullable) &&
 			bms_is_subset(ukey->eclass_indexes, ecs))
 			return true;