Several routines in setrefs.c would crash on array refs

due to lack of check for recursing into a null subexpression.

src/backend/optimizer/plan/setrefs.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/plan/setrefs.c,v 1.42 1999/04/26 00:37:46 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/plan/setrefs.c,v 1.43 1999/04/29 00:20:27 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -747,6 +747,9 @@ replace_agg_clause(Node *clause, List *subplanTargetList)
 	List	   *t;
 	List	   *agg_list = NIL;
 
+	if (clause == NULL)
+		return NIL;
+
 	if (IsA(clause, Var))
 	{
 		TargetEntry *subplanVar;
@@ -864,6 +867,9 @@ del_agg_clause(Node *clause)
 {
 	List	   *t;
 
+	if (clause == NULL)
+		return clause;
+
 	if (IsA(clause, Var))
 		return clause;
 	else if (is_funcclause(clause))
@@ -942,6 +948,9 @@ check_having_qual_for_vars(Node *clause, List *targetlist_so_far)
 {
 	List	   *t;
 
+	if (clause == NULL)
+		return targetlist_so_far;
+
 	if (IsA(clause, Var))
 	{
 		RelOptInfo	tmp_rel;
@@ -1035,6 +1044,9 @@ check_having_for_ungrouped_vars(Node *clause, List *groupClause)
 {
 	List	   *t;
 
+	if (clause == NULL)
+		return;
+
 	if (IsA(clause, Var))
 	{
 		/* Ignore vars elsewhere in the having clause, since the