diff --git a/agpl-cr-mutable_assignment.adb b/agpl-cr-mutable_assignment.adb
index fe9a35c..1c7796f 100644
--- a/agpl-cr-mutable_assignment.adb
+++ b/agpl-cr-mutable_assignment.adb
@@ -45,7 +45,7 @@ with Ada.Numerics.Generic_Elementary_Functions;
 
 package body Agpl.Cr.Mutable_Assignment is
 
-   Expensive_Checks : constant Boolean := True;
+   Expensive_Checks : constant Boolean := False;
 
    File : constant String := "[Mutable_Assignment] ";
 
diff --git a/agpl-htn-plan-utils.adb b/agpl-htn-plan-utils.adb
index ad1c654..5fe493a 100644
--- a/agpl-htn-plan-utils.adb
+++ b/agpl-htn-plan-utils.adb
@@ -74,8 +74,11 @@ package body Agpl.Htn.Plan.Utils is
       Parent         : Subplan;
       Reindex_Needed : Boolean := False;
    begin
-      pragma Assert (Get_Kind (Node) = Task_Node);
-      loop
+      if Node /= null then
+         pragma Assert (Get_Kind (Node) = Task_Node);
+         null;
+      end if;
+      while Node /= null loop
          if Get_Kind (Node) = Or_Node then
             Parent := Get_Parent (Node);
             --  Replace the OR node by the branch we were arriving from.
diff --git a/agpl-htn-plan.adb b/agpl-htn-plan.adb
index 38e6329..5dc115d 100644
--- a/agpl-htn-plan.adb
+++ b/agpl-htn-plan.adb
@@ -401,7 +401,11 @@ package body Agpl.Htn.Plan is
    is
       use Plan_Node.Task_Id_To_Node;
    begin
-      return Element (Find (This.Index, Id));
+      if This.Index.Contains (Id) then
+         return This.Index.Element (Id);
+      else
+         return null;
+      end if;
    end Get_Node;
 
    --------------
diff --git a/agpl-htn-plan.ads b/agpl-htn-plan.ads
index c0bcc60..28d86fb 100644
--- a/agpl-htn-plan.ads
+++ b/agpl-htn-plan.ads
@@ -111,6 +111,7 @@ package Agpl.Htn.Plan is
      (This : in Object;
       Id   : in Tasks.Task_Id) return Subplan;
    --  Get the branch starting at the given task.
+   --  May be null if the task isn't in the tree
 
    function Get_Root (This : in Object) return Subplan;
    --  Get the root node.