lib: fix return value of separate for nil seq.

* lib.c (separate): Return (list nil nil) instead of just nil
when the sequence parameter is nil, as is documented.

1 files changed, 1 insertions, 1 deletions

diff --git a/lib.c b/lib.c
index 2f3f6603..51092c36 100644
--- a/lib.c
+++ b/lib.c
@@ -3153,7 +3153,7 @@ val separate(val pred, val seq_in, val keyfun_in)
 
   switch (type(seq_in)) {
   case NIL:
-    return nil;
+    return cons(nil, cons(nil, nil));
   case CONS:
   case LCONS:
   case COBJ: