X-Git-Url: http://nitlanguage.org

diff --git a/lib/trees/abstract_tree.nit b/lib/trees/abstract_tree.nit
index 63ac67a..d05663e 100644
--- a/lib/trees/abstract_tree.nit
+++ b/lib/trees/abstract_tree.nit
@@ -28,7 +28,7 @@ abstract class TreeMap[K: Comparable, E]
 	protected type N: TreeNode[K, E]
 
 	# The `root` node of the tree (null if tree is empty)
-	protected var root: nullable N protected writable = null
+	protected var root: nullable N = null is protected writable
 
 	# Display the tree in a gaphical windows
 	# Graphviz with a working -Txlib is expected
@@ -51,9 +51,9 @@ class TreeNode[K: Comparable, E]
 	var value: E
 
 	# Direct parent of this node (null if the node is root)
-	var parent: nullable SELF writable = null
+	var parent: nullable SELF = null is writable
 
-	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`