diff --git a/duniter4j-core-shared/src/main/java/org/duniter/core/util/merkle/MerkleTree.java b/duniter4j-core-shared/src/main/java/org/duniter/core/util/merkle/MerkleTree.java
index c4ece2c2f47e0ef61192a4807bc2f16a2b8e47a2..5a3b15e93afdb470f1dcf7145651bcc01d97d003 100644
--- a/duniter4j-core-shared/src/main/java/org/duniter/core/util/merkle/MerkleTree.java
+++ b/duniter4j-core-shared/src/main/java/org/duniter/core/util/merkle/MerkleTree.java
@@ -142,6 +142,7 @@ public class MerkleTree {
     }
 
     public String root() {
+        if (nodesCount == 0) return null; // No leaves
         return rows.get(0).get(0);
     }