set Print.values to NULL if there are no values

Python/ast.c

@@ -2144,9 +2144,9 @@ ast_for_print_stmt(struct compiling *c, const node *n)
                              | '>>' test [ (',' test)+ [','] ] )
      */
     expr_ty dest = NULL, expression;
-    asdl_seq *seq;
+    asdl_seq *seq = NULL;
     bool nl;
-    int i, j, start = 1;
+    int i, j, values_count, start = 1;
 
     REQ(n, print_stmt);
     if (NCH(n) >= 2 && TYPE(CHILD(n, 1)) == RIGHTSHIFT) {
@@ -2155,14 +2155,17 @@ ast_for_print_stmt(struct compiling *c, const node *n)
             return NULL;
             start = 4;
     }
-    seq = asdl_seq_new((NCH(n) + 1 - start) / 2, c->c_arena);
-    if (!seq)
-        return NULL;
-    for (i = start, j = 0; i < NCH(n); i += 2, ++j) {
-        expression = ast_for_expr(c, CHILD(n, i));
-        if (!expression)
+    values_count = (NCH(n) + 1 - start) / 2;
+    if (values_count) {
+        seq = asdl_seq_new(values_count, c->c_arena);
+        if (!seq)
             return NULL;
-        asdl_seq_SET(seq, j, expression);
+        for (i = start, j = 0; i < NCH(n); i += 2, ++j) {
+            expression = ast_for_expr(c, CHILD(n, i));
+            if (!expression)
+                return NULL;
+            asdl_seq_SET(seq, j, expression);
+        }
     }
     nl = (TYPE(CHILD(n, NCH(n) - 1)) == COMMA) ? false : true;
     return Print(dest, seq, nl, LINENO(n), n->n_col_offset, c->c_arena);