isl_convex_hull.c: extend: check hull argument

diff --git a/isl_convex_hull.c b/isl_convex_hull.c
index b634353..297ae19 100644 (file)
--- a/isl_convex_hull.c
+++ b/isl_convex_hull.c
@@ -682,6 +682,9 @@ static struct isl_basic_set *extend(struct isl_basic_set *hull,
        struct isl_basic_set *hull_facet = NULL;
        unsigned dim;
 
+       if (!hull)
+               return NULL;
+
        isl_assert(set->ctx, set->n > 0, goto error);
 
        dim = isl_set_n_dim(set);