diff --git a/.travis.yml b/.travis.yml
index 52fa5db..c0110b2 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,4 +1,6 @@
 language: java
+jdk:
+  - openjdk8
 script: mvn -f json-overlay/pom.xml test
 cache:
   directories:
diff --git a/json-overlay/src/main/java/com/reprezen/jsonoverlay/ListOverlay.java b/json-overlay/src/main/java/com/reprezen/jsonoverlay/ListOverlay.java
index ef9e563..64b2d7a 100644
--- a/json-overlay/src/main/java/com/reprezen/jsonoverlay/ListOverlay.java
+++ b/json-overlay/src/main/java/com/reprezen/jsonoverlay/ListOverlay.java
@@ -36,9 +36,14 @@ private ListOverlay(JsonNode json, JsonOverlay<?> parent, OverlayFactory<List<V>
 
 	private ListOverlay(List<V> value, JsonOverlay<?> parent, OverlayFactory<List<V>> factory,
 			ReferenceManager refMgr) {
-		super(new ArrayList<>(value), parent, factory, refMgr);
+		super(copyValue(value), parent, factory, refMgr);
 		this.itemFactory = ((ListOverlayFactory<V>) factory).getItemFactory();
 	}
+	static <T> List<T> copyValue(List<T> src) {
+		if (src == null)
+			return null;
+		return new ArrayList<>(src);
+	}
 
 	@Override
 	protected JsonOverlay<?> _findInternal(JsonPointer path) {
diff --git a/json-overlay/src/main/java/com/reprezen/jsonoverlay/MapOverlay.java b/json-overlay/src/main/java/com/reprezen/jsonoverlay/MapOverlay.java
index f045a97..3023f05 100644
--- a/json-overlay/src/main/java/com/reprezen/jsonoverlay/MapOverlay.java
+++ b/json-overlay/src/main/java/com/reprezen/jsonoverlay/MapOverlay.java
@@ -43,13 +43,19 @@ private MapOverlay(JsonNode json, JsonOverlay<?> parent, OverlayFactory<Map<Stri
 
 	private MapOverlay(Map<String, V> value, JsonOverlay<?> parent, OverlayFactory<Map<String, V>> factory,
 			ReferenceManager refMgr) {
-		super(new LinkedHashMap<>(value), parent, factory, refMgr);
+		super(copyValue(value), parent, factory, refMgr);
 		MapOverlayFactory<V> mapOverlayFactory = (MapOverlayFactory<V>) factory;
 		this.valueFactory = mapOverlayFactory.getValueFactory();
 		String keyPattern = mapOverlayFactory.getKeyPattern();
 		this.keyPattern = keyPattern != null ? Pattern.compile(keyPattern) : null;
 	}
 
+	static <T> Map<String, T> copyValue(Map<String, T> src) {
+		if (src == null)
+			return null;
+		return new LinkedHashMap<>(src);
+	}
+
 	@Override
 	protected JsonOverlay<?> _findInternal(JsonPointer path) {
 		String key = path.getMatchingProperty();