update code to comply with new superstring policy

[nit.git] / lib / trees / abstract_tree.nit

diff --git a/lib/trees/abstract_tree.nit b/lib/trees/abstract_tree.nit
index 63ac67a..0b79490 100644 (file)
--- a/lib/trees/abstract_tree.nit
+++ b/lib/trees/abstract_tree.nit
@@ -53,7 +53,7 @@ class TreeNode[K: Comparable, E]
        # Direct parent of this node (null if the node is root)
        var parent: nullable SELF writable = null
 
-       redef fun to_s do return "\{{value}\}"
+       redef fun to_s do return "\{{value or else ""}\}"
 
        # Return dot representation of this node
        # Used for debugging by `AbstractTree::show_dot`