#6 Mapping null collections as null instead of an empty collection

processor/src/main/resources/mapper-implementation.ftl

@@ -38,7 +38,7 @@ public class ${implementationName} implements ${interfaceName} {
     @Override
     public ${beanMapping.targetType.name}<${beanMapping.targetType.elementType.name}> ${beanMapping.mappingMethod.name}(${beanMapping.sourceType.name}<${beanMapping.sourceType.elementType.name}> ${beanMapping.mappingMethod.parameterName}) {
         if( ${beanMapping.mappingMethod.parameterName} == null ) {
-            return new ${beanMapping.targetType.name}<${beanMapping.targetType.elementType.name}>();
+            return null;
         }
 
         ${beanMapping.targetType.name}<${beanMapping.targetType.elementType.name}> ${beanMapping.targetType.name?uncap_first} = new ${beanMapping.targetType.name}<${beanMapping.targetType.elementType.name}>();
@@ -87,7 +87,7 @@ public class ${implementationName} implements ${interfaceName} {
     @Override
     public ${beanMapping.sourceType.name}<${beanMapping.sourceType.elementType.name}> ${beanMapping.reverseMappingMethod.name}(${beanMapping.targetType.name}<${beanMapping.targetType.elementType.name}> ${beanMapping.reverseMappingMethod.parameterName}) {
         if( ${beanMapping.reverseMappingMethod.parameterName} == null ) {
-            return new ${beanMapping.sourceType.name}<${beanMapping.sourceType.elementType.name}>();
+            return null;
         }
 
         ${beanMapping.sourceType.name}<${beanMapping.sourceType.elementType.name}> ${beanMapping.sourceType.name?uncap_first} = new ${beanMapping.sourceType.name}<${beanMapping.sourceType.elementType.name}>();

processor/src/test/java/org/mapstruct/ap/test/collection/CollectionMappingTest.java

@@ -0,0 +1,48 @@
+/**
+ *  Copyright 2012-2013 Gunnar Morling (http://www.gunnarmorling.de/)
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.collection;
+
+import java.util.Arrays;
+import java.util.List;
+
+import org.mapstruct.ap.testutil.IssueKey;
+import org.mapstruct.ap.testutil.MapperTestBase;
+import org.testng.annotations.Test;
+
+import static org.fest.assertions.Assertions.assertThat;
+
+public class CollectionMappingTest extends MapperTestBase {
+
+    @Override
+    protected List<Class<?>> getTestClasses() {
+        return Arrays.<Class<?>>asList(
+            Source.class,
+            Target.class,
+            SourceTargetMapper.class
+        );
+    }
+
+    @Test
+    @IssueKey("6")
+    public void shouldMapNullList() {
+        Source source = new Source();
+
+        Target target = SourceTargetMapper.INSTANCE.sourceToTarget( source );
+
+        assertThat( target ).isNotNull();
+        assertThat( target.getStringList() ).isNull();
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/collection/Source.java

@@ -0,0 +1,31 @@
+/**
+ *  Copyright 2012-2013 Gunnar Morling (http://www.gunnarmorling.de/)
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.collection;
+
+import java.util.List;
+
+public class Source {
+
+    private List<String> stringList;
+
+    public List<String> getStringList() {
+        return stringList;
+    }
+
+    public void setStringList(List<String> stringList) {
+        this.stringList = stringList;
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/collection/SourceTargetMapper.java

@@ -0,0 +1,28 @@
+/**
+ *  Copyright 2012-2013 Gunnar Morling (http://www.gunnarmorling.de/)
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.collection;
+
+
+import org.mapstruct.Mapper;
+import org.mapstruct.Mappers;
+
+@Mapper
+public interface SourceTargetMapper {
+
+    public static SourceTargetMapper INSTANCE = Mappers.getMapper( SourceTargetMapper.class );
+
+    Target sourceToTarget(Source source);
+}

processor/src/test/java/org/mapstruct/ap/test/collection/Target.java

@@ -0,0 +1,31 @@
+/**
+ *  Copyright 2012-2013 Gunnar Morling (http://www.gunnarmorling.de/)
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.collection;
+
+import java.util.List;
+
+public class Target {
+
+    private List<String> stringList;
+
+    public List<String> getStringList() {
+        return stringList;
+    }
+
+    public void setStringList(List<String> stringList) {
+        this.stringList = stringList;
+    }
+}