fix: Merkle tree: do not try to read rows if no one exists

duniter4j-core-shared/src/test/java/org/duniter/core/util/merkle/MerkleTreeTest.java

@@ -25,15 +25,11 @@ package org.duniter.core.util.merkle;
 import com.google.common.collect.ImmutableList;
 import org.junit.Assert;
 import org.junit.Test;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
 
 import java.util.List;
 
 public class MerkleTreeTest {
 
-    private static final Logger log = LoggerFactory.getLogger(MerkleTreeTest.class);
-
     @Test
     public void createMerkleTree() {
 
@@ -136,4 +132,20 @@ public class MerkleTreeTest {
         Assert.assertEquals(6, tree.depth());
         Assert.assertEquals(38, tree.nodes());
     }
+
+
+    @Test
+    public void createEmptyMerkleTree() {
+
+        MerkleTree tree;
+        List<String> emptyList = ImmutableList.of();
+
+        // SHA1
+        {
+            tree = new MerkleTree("sha1", emptyList, true);
+            Assert.assertNotNull(tree);
+            Assert.assertNull(tree.root());
+
+        }
+    }
 }