Fixed #691

Author: cowtowncoder

release-notes/CREDITS

@@ -203,3 +203,7 @@ Zoltan Farkas (zolyfarkas@github)
 Ludevik@github:
   * Reported #682: Class<?>-valued Map keys not serialized properly
    (2.5.1)
+
+Antibrumm@github:
+  * Reported #691: Jackson 2.5.0. NullSerializer for MapProperty failing
+   (2.5.2)

release-notes/VERSION

@@ -4,6 +4,11 @@ Project: jackson-databind
 === Releases ===
 ------------------------------------------------------------------------
 
+2.5.2 (not yet released)
+
+#691: Jackson 2.5.0. NullSerializer for MapProperty failing
+ (reported by Antibrumm@github)
+
 2.5.1 (06-Feb-2015)
 
 #667: Problem with bogus conflict between single-arg-String vs `CharSequence` constructor

src/main/java/com/fasterxml/jackson/databind/ser/std/MapSerializer.java

@@ -772,8 +772,6 @@ protected void serializeTypedFields(Map<?,?> value, JsonGenerator gen, Serialize
                     continue;
                 }
                 valueSer = provider.getDefaultNullValueSerializer();
-                keySerializer.serialize(keyElem, gen, provider);
-                provider.defaultSerializeNull(gen);
             } else {
                 valueSer = _valueSerializer;
                 Class<?> cc = valueElem.getClass();

src/main/java/com/fasterxml/jackson/databind/ser/std/NullSerializer.java

@@ -7,6 +7,7 @@
 import com.fasterxml.jackson.databind.*;
 import com.fasterxml.jackson.databind.annotation.JacksonStdImpl;
 import com.fasterxml.jackson.databind.jsonFormatVisitors.JsonFormatVisitorWrapper;
+import com.fasterxml.jackson.databind.jsontype.TypeSerializer;
 
 /**
  * This is a simple dummy serializer that will just output literal
@@ -25,8 +26,22 @@ public class NullSerializer
     private NullSerializer() { super(Object.class); }
 
     @Override
-    public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider) throws IOException {
-        jgen.writeNull();
+    public void serialize(Object value, JsonGenerator gen, SerializerProvider provider) throws IOException {
+        gen.writeNull();
+    }
+
+    /**
+     * Although this method should rarely get called, for convenience we should override
+     * it, and handle it same way as "natural" types: by serializing exactly as is,
+     * without type decorations. The most common possible use case is that of delegation
+     * by JSON filter; caller can not know what kind of serializer it gets handed.
+     */
+    @Override
+    public void serializeWithType(Object value, JsonGenerator gen, SerializerProvider serializers,
+            TypeSerializer typeSer)
+        throws IOException
+    {
+        gen.writeNull();
     }
 
     @Override

src/test/java/com/fasterxml/jackson/databind/ser/TestMapSerialization.java

@@ -125,6 +125,9 @@ public NoEmptyStringsMap add(String key, String value) {
     @JsonTypeName("mymap")
     static class MapWithTypedValues extends LinkedHashMap<String,String> { }
 
+    @JsonTypeInfo(use = Id.CLASS)
+    public static class Mixin691 { }
+
     /*
     /**********************************************************
     /* Test methods
@@ -276,4 +279,16 @@ public void testNullJsonMapping691() throws Exception
         assertEquals(aposToQuotes("{'@type':'mymap','id':'Test','NULL':null}"),
                 json);
     }    
+
+    // [databind#691]
+    public void testNullJsonInTypedMap691() throws Exception {
+        Map<String, String> map = new HashMap<String, String>();
+        map.put("NULL", null);
+    
+        ObjectMapper mapper = new ObjectMapper();
+        mapper.addMixIn(Object.class, Mixin691.class);
+        String json = mapper.writeValueAsString(map);
+        assertEquals("{\"@class\":\"java.util.HashMap\",\"NULL\":null}", json);
+    }
 }
+