From 17fe0f4bca746d3f94335585c5ce8a757edfa8cc Mon Sep 17 00:00:00 2001
From: Florian Habermann <f.habermann@cyrock.ai>
Date: Mon, 5 Oct 2026 13:37:50 +0200
Subject: [PATCH] Fix HashMapIdObject.toString() on an empty map

toString() always deleted the trailing ", " separator and replaced the last char with '}'. On an empty map the buffer only held "{", so deleteLast() emptied it and setLast() threw StringIndexOutOfBoundsException. An empty map now returns "{}".
---
 .../collections/HashMapIdObject.java          |  5 ++
 .../collections/HashMapIdObjectTest.java      | 46 +++++++++++++++++++
 2 files changed, 51 insertions(+)
 create mode 100644 integration-tests/src/test/java/org/eclipse/serializer/collections/HashMapIdObjectTest.java

diff --git a/base/src/main/java/org/eclipse/serializer/collections/HashMapIdObject.java b/base/src/main/java/org/eclipse/serializer/collections/HashMapIdObject.java
index 6d7bd121..e726c053 100644
--- a/base/src/main/java/org/eclipse/serializer/collections/HashMapIdObject.java
+++ b/base/src/main/java/org/eclipse/serializer/collections/HashMapIdObject.java
@@ -296,6 +296,11 @@ public final int iterateValues(final Consumer<? super E> procedure)
 	@Override
 	public final String toString()
 	{
+		if(this.size == 0)
+		{
+			return "{}";
+		}
+
 		final VarString vc = VarString.New().add('{');
 		for(Entry<E> entry : this.hashSlots)
 		{
diff --git a/integration-tests/src/test/java/org/eclipse/serializer/collections/HashMapIdObjectTest.java b/integration-tests/src/test/java/org/eclipse/serializer/collections/HashMapIdObjectTest.java
new file mode 100644
index 00000000..64022f01
--- /dev/null
+++ b/integration-tests/src/test/java/org/eclipse/serializer/collections/HashMapIdObjectTest.java
@@ -0,0 +1,46 @@
+package org.eclipse.serializer.collections;
+
+/*-
+ * #%L
+ * Eclipse Serializer Integration Tests
+ * %%
+ * Copyright (C) 2023 - 2026 MicroStream Software
+ * %%
+ * This program and the accompanying materials are made
+ * available under the terms of the Eclipse Public License 2.0
+ * which is available at https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ * #L%
+ */
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class HashMapIdObjectTest
+{
+	@Test
+	void toString_emptyMap()
+	{
+		// regression: threw StringIndexOutOfBoundsException
+		assertEquals("{}", HashMapIdObject.New().toString());
+	}
+
+	@Test
+	void toString_singleEntry()
+	{
+		final HashMapIdObject<String> map = HashMapIdObject.New();
+		map.add(1L, "a");
+		assertEquals("{1 -> a}", map.toString());
+	}
+
+	@Test
+	void toString_afterClear()
+	{
+		final HashMapIdObject<String> map = HashMapIdObject.New();
+		map.add(1L, "a");
+		map.clear();
+		assertEquals("{}", map.toString());
+	}
+}