Fixed njs_array_expand() for empty arrays.
diff --git a/src/njs_array.c b/src/njs_array.c
index 2367420..6691d80 100644
--- a/src/njs_array.c
+++ b/src/njs_array.c
@@ -408,7 +408,9 @@
 
     array->start = start;
 
-    njs_mp_free(vm->mem_pool, old);
+    if (old != NULL) {
+        njs_mp_free(vm->mem_pool, old);
+    }
 
     return NJS_OK;