diff --git a/spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/intTest/java/org/springframework/boot/maven/JarIntegrationTests.java b/spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/intTest/java/org/springframework/boot/maven/JarIntegrationTests.java
index c2c2b79d695..baa5238b33b 100644
--- a/spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/intTest/java/org/springframework/boot/maven/JarIntegrationTests.java
+++ b/spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/intTest/java/org/springframework/boot/maven/JarIntegrationTests.java
@@ -402,6 +402,7 @@ class JarIntegrationTests extends AbstractArchiveIntegrationTests {
 			while (line != null) {
 				if (line.startsWith("- ")) {
 					layer = line.substring(3, line.length() - 2);
+					index.put(layer, new ArrayList<>());
 				}
 				else if (line.startsWith("  - ")) {
 					index.computeIfAbsent(layer, (key) -> new ArrayList<>()).add(line.substring(5, line.length() - 1));