When start an anonymous transaction in a transaction then a new transaction is created

src/main/java/net/kemitix/gitdb/impl/GitDBTransactionImpl.java

@@ -64,8 +64,8 @@ class GitDBTransactionImpl implements GitDBTransaction {
     }
 
     @Override
-    public GitDBTransaction transaction() {
+    public GitDBTransaction transaction() throws IOException {
-        return null;
+        return branch.transaction();
     }
 
     @Override

src/test/java/net/kemitix/gitdb/test/GitDBTest.java

@@ -448,6 +448,19 @@ class GitDBTest implements WithAssertions {
         assertThat(result).contains(value);
     }
 
+    // When start an anonymous transaction in a transaction then a new transaction is created
+    @Test
+    void startAnonymousTransaction_whenTransaction_thenReturnAnotherTransaction() throws IOException {
+        //given
+        final GitDBBranch initialBranch = gitDBBranch();
+        final GitDBTransaction firstTransaction = initialBranch.transaction();
+        //when
+        final GitDBTransaction secondTransaction = firstTransaction.transaction();
+        //then
+        assertThat(secondTransaction).isNotNull();
+        assertThat(secondTransaction).isNotSameAs(firstTransaction);
+    }
+
     // Given a GitDbTransaction handle with a added, updated and removed keys
     // When closing the transaction an GitDbBranch is returned
     // When closing the transaction the added key/value is found