Nested Map should not bind to null

Fixes gh-9801

Author: mbhave

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

@@ -298,11 +298,10 @@ private Object bindBean(ConfigurationPropertyName name, Bindable<?> target,
 		}
 		BeanPropertyBinder propertyBinder = (propertyName, propertyTarget) -> bind(
 				name.append(propertyName), propertyTarget, handler, context);
-		Class<?> type = target.getType().resolve();
-		if (context.hasBoundBean(type)) {
+		if (context.isProcessingName(name)) {
 			return null;
 		}
-		return context.withBean(type, () -> {
+		return context.withName(name, () -> {
 			Stream<?> boundBeans = BEAN_BINDERS.stream()
 					.map((b) -> b.bind(name, target, context, propertyBinder));
 			return boundBeans.filter(Objects::nonNull).findFirst().orElse(null);
@@ -353,7 +352,7 @@ final class Context implements BindContext {
 		private final List<ConfigurationPropertySource> source = Arrays
 				.asList((ConfigurationPropertySource) null);
 
-		private final Deque<Class<?>> beans = new ArrayDeque<>();
+		private final Deque<ConfigurationPropertyName> names = new ArrayDeque<>();
 
 		private ConfigurationProperty configurationProperty;
 
@@ -385,13 +384,13 @@ public <T> T withSource(ConfigurationPropertySource source,
 			}
 		}
 
-		public <T> T withBean(Class<?> bean, Supplier<T> supplier) {
-			this.beans.push(bean);
+		public <T> T withName(ConfigurationPropertyName name, Supplier<T> supplier) {
+			this.names.push(name);
 			try {
 				return withIncreasedDepth(supplier);
 			}
 			finally {
-				this.beans.pop();
+				this.names.pop();
 			}
 		}
 
@@ -421,8 +420,8 @@ public Stream<ConfigurationPropertySource> streamSources() {
 			return StreamSupport.stream(Binder.this.sources.spliterator(), false);
 		}
 
-		public boolean hasBoundBean(Class<?> bean) {
-			return this.beans.contains(bean);
+		public boolean isProcessingName(ConfigurationPropertyName name) {
+			return this.names.contains(name);
 		}
 
 		@Override

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

@@ -19,7 +19,9 @@
 import java.time.LocalDate;
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.LinkedHashMap;
 import java.util.List;
+import java.util.Map;
 
 import org.assertj.core.matcher.AssertionMatcher;
 import org.junit.Before;
@@ -237,6 +239,19 @@ public void assertion(BindException ex) throws AssertionError {
 		this.binder.bind("foo", target);
 	}
 
+	@Test
+	public void nestedMapsShouldNotBindToNull() throws Exception {
+		MockConfigurationPropertySource source = new MockConfigurationPropertySource();
+		source.put("foo.value", "one");
+		source.put("foo.foos.foo1.value", "two");
+		source.put("foo.foos.foo2.value", "three");
+		this.sources.add(source);
+		BindResult<Foo> foo = this.binder.bind("foo", Foo.class);
+		assertThat(foo.get().getValue()).isNotNull();
+		assertThat(foo.get().getFoos().get("foo1").getValue()).isEqualTo("two");
+		assertThat(foo.get().getFoos().get("foo2").getValue()).isEqualTo("three");
+	}
+
 	public static class JavaBean {
 
 		private String value;
@@ -263,4 +278,24 @@ public enum ExampleEnum {
 
 	}
 
+	static class Foo {
+
+		private String value;
+
+		private Map<String, Foo> foos = new LinkedHashMap<>();
+
+		public Map<String, Foo> getFoos() {
+			return this.foos;
+		}
+
+		public String getValue() {
+			return this.value;
+		}
+
+		public void setValue(String value) {
+			this.value = value;
+		}
+
+	}
+
 }