Don't fail if aggregate merge can't get existing value

Fixes gh-13303

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/bind/CollectionBinder.java

@@ -55,10 +55,9 @@ class CollectionBinder extends IndexedElementsBinder<Collection<Object>> {
 	}
 
 	@Override
-	@SuppressWarnings("unchecked")
 	protected Collection<Object> merge(Supplier<?> existing,
 			Collection<Object> additional) {
-		Collection<Object> existingCollection = (Collection<Object>) existing.get();
+		Collection<Object> existingCollection = getExistingIfPossible(existing);
 		if (existingCollection == null) {
 			return additional;
 		}
@@ -72,6 +71,16 @@ class CollectionBinder extends IndexedElementsBinder<Collection<Object>> {
 		}
 	}
 
+	@SuppressWarnings("unchecked")
+	private Collection<Object> getExistingIfPossible(Supplier<?> existing) {
+		try {
+			return (Collection<Object>) existing.get();
+		}
+		catch (Exception ex) {
+			return null;
+		}
+	}
+
 	private Collection<Object> copyIfPossible(Collection<Object> collection) {
 		try {
 			return createNewCollection(collection);

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/bind/MapBinder.java

@@ -83,10 +83,9 @@ class MapBinder extends AggregateBinder<Map<Object, Object>> {
 	}
 
 	@Override
-	@SuppressWarnings("unchecked")
 	protected Map<Object, Object> merge(Supplier<?> existing,
 			Map<Object, Object> additional) {
-		Map<Object, Object> existingMap = (Map<Object, Object>) existing.get();
+		Map<Object, Object> existingMap = getExistingIfPossible(existing);
 		if (existingMap == null) {
 			return additional;
 		}
@@ -101,6 +100,16 @@ class MapBinder extends AggregateBinder<Map<Object, Object>> {
 		}
 	}
 
+	@SuppressWarnings("unchecked")
+	private Map<Object, Object> getExistingIfPossible(Supplier<?> existing) {
+		try {
+			return (Map<Object, Object>) existing.get();
+		}
+		catch (Exception ex) {
+			return null;
+		}
+	}
+
 	private Map<Object, Object> copyIfPossible(Map<Object, Object> map) {
 		try {
 			return createNewMap(map.getClass(), map);

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/bind/CollectionBinderTests.java

@@ -417,6 +417,16 @@ public class CollectionBinderTests {
 		assertThat(bean.getBar()).containsExactly("hello");
 	}
 
+	@Test
+	public void bindToBeanWithExceptionInGetterForExistingValue() {
+		MockConfigurationPropertySource source = new MockConfigurationPropertySource();
+		source.put("foo.values", "a,b,c");
+		this.sources.add(source);
+		BeanWithGetterException result = this.binder
+				.bind("foo", Bindable.of(BeanWithGetterException.class)).get();
+		assertThat(result.getValues()).containsExactly("a", "b", "c");
+	}
+
 	public static class ExampleCollectionBean {
 
 		private List<String> items = new ArrayList<>();
@@ -521,4 +531,18 @@ public class CollectionBinderTests {
 
 	}
 
+	public static class BeanWithGetterException {
+
+		private List<String> values;
+
+		public void setValues(List<String> values) {
+			this.values = values;
+		}
+
+		public List<String> getValues() {
+			return Collections.unmodifiableList(this.values);
+		}
+
+	}
+
 }

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/bind/MapBinderTests.java

@@ -631,6 +631,16 @@ public class MapBinderTests {
 				entry("e", "f"));
 	}
 
+	@Test
+	public void bindToBeanWithExceptionInGetterForExistingValue() {
+		MockConfigurationPropertySource source = new MockConfigurationPropertySource();
+		source.put("foo.values.a", "b");
+		this.sources.add(source);
+		BeanWithGetterException result = this.binder
+				.bind("foo", Bindable.of(BeanWithGetterException.class)).get();
+		assertThat(result.getValues()).containsExactly(entry("a", "b"));
+	}
+
 	private <K, V> Bindable<Map<K, V>> getMapBindable(Class<K> keyGeneric,
 			ResolvableType valueType) {
 		ResolvableType keyType = ResolvableType.forClass(keyGeneric);
@@ -736,4 +746,18 @@ public class MapBinderTests {
 
 	}
 
+	public static class BeanWithGetterException {
+
+		private Map<String, String> values;
+
+		public void setValues(Map<String, String> values) {
+			this.values = values;
+		}
+
+		public Map<String, String> getValues() {
+			return Collections.unmodifiableMap(this.values);
+		}
+
+	}
+
 }