lib/ai/backtrack: add a missing assert

or else the possible null will loop and cause errors.

Signed-off-by: Jean Privat <jean@pryen.org>

diff --git a/lib/ai/backtrack.nit b/lib/ai/backtrack.nit
index 550df10..ddc68ef 100644 (file)
--- a/lib/ai/backtrack.nit
+++ b/lib/ai/backtrack.nit
@@ -209,6 +209,7 @@ class BacktrackSolver[S: Object, A]
 
                                problem.backtrack(state, a)
                                node = node.parent
+                               assert node != null
                                continue
                        end