DATADOC-259 - Fixed potential NullPointerException in MapingMongoConverter.writeMapInternal(…).

MappingMongoConverter.writeInternal(…) invoked ….writeMapInternal(…) handing in null for the TypeInformation which violated the implicit contract for the method. Made contract explicit in Javadoc and hand in plain Map TypeInformation.

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/MappingMongoConverter.java

@@ -75,6 +75,8 @@ import org.springframework.util.StringUtils;
 public class MappingMongoConverter extends AbstractMongoConverter implements ApplicationContextAware,
 		TypeMapperProvider {
 
+	@SuppressWarnings("rawtypes")
+	private static final TypeInformation<Map> MAP_TYPE_INFORMATION = ClassTypeInformation.from(Map.class);
 	private static final List<Class<?>> VALID_ID_TYPES = Arrays.asList(new Class<?>[] { ObjectId.class, String.class,
 			BigInteger.class, byte[].class });
 
@@ -325,7 +327,7 @@ public class MappingMongoConverter extends AbstractMongoConverter implements App
 		}
 
 		if (Map.class.isAssignableFrom(obj.getClass())) {
-			writeMapInternal((Map<Object, Object>) obj, dbo, null);
+			writeMapInternal((Map<Object, Object>) obj, dbo, MAP_TYPE_INFORMATION);
 			return;
 		}
 
@@ -552,6 +554,13 @@ public class MappingMongoConverter extends AbstractMongoConverter implements App
 		return dbList;
 	}
 
+	/**
+	 * Writes the given {@link Map} to the given {@link DBObject} considering the given {@link TypeInformation}.
+	 * 
+	 * @param obj must not be {@literal null}.
+	 * @param dbo must not be {@literal null}.
+	 * @param propertyType must not be {@literal null}.
+	 */
 	protected void writeMapInternal(Map<Object, Object> obj, DBObject dbo, TypeInformation<?> propertyType) {
 		for (Map.Entry<Object, Object> entry : obj.entrySet()) {
 			Object key = entry.getKey();
@@ -586,7 +595,7 @@ public class MappingMongoConverter extends AbstractMongoConverter implements App
 	 */
 	protected void addCustomTypeKeyIfNecessary(TypeInformation<?> type, Object value, DBObject dbObject) {
 
-		if (type == null) {
+		if (type == null || type.getActualType() == null) {
 			return;
 		}
 

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/convert/MappingMongoConverterUnitTests.java

@@ -712,6 +712,26 @@ public class MappingMongoConverterUnitTests {
 		assertThat(wrapper.listOfMaps.get(0).get("Foo"), is(Locale.ENGLISH));
 	}
 
+	/**
+	 * @see DATADOC-259
+	 */
+	@Test
+	public void writesPlainMapOfCollectionsCorrectly() {
+		
+		Map<String,List<Locale>> map = Collections.singletonMap("Foo", Arrays.asList(Locale.US));
+		DBObject result = new BasicDBObject();
+		converter.write(map, result);
+		
+		assertThat(result.containsField("Foo"), is(true));
+		assertThat(result.get("Foo"), is(notNullValue()));
+		assertThat(result.get("Foo"), is(BasicDBList.class));
+		
+		BasicDBList list = (BasicDBList) result.get("Foo");
+		
+		assertThat(list.size(), is(1));
+		assertThat(list.get(0), is((Object) Locale.US.toString()));
+	}
+	
 	class GenericType<T> {
 		T content;
 	}