Fix #1437

Author: cowtowncoder

src/main/java/com/fasterxml/jackson/databind/deser/impl/MergingSettableBeanProperty.java

@@ -10,8 +10,12 @@
 /**
  * {@link SettableBeanProperty} implementation that will try to access value of
  * the property first, and if non-null value found, pass that for update
- * (using {@link com.fasterxml.jackson.databind.JsonDeserializer#deserialize(com.fasterxml.jackson.core.JsonParser, com.fasterxml.jackson.databind.DeserializationContext, Object)}
- * ) instead of constructing a new value. This is necessary to support "merging" properties.
+ * (using {@link com.fasterxml.jackson.databind.JsonDeserializer#deserialize(com.fasterxml.jackson.core.JsonParser, com.fasterxml.jackson.databind.DeserializationContext, Object)})
+ * instead of constructing a new value. This is necessary to support "merging" properties.
+ *<p>
+ * Note that there are many similarities to {@link SetterlessProperty}, which predates
+ * this variant; and that one is even used in cases where there is no mutator
+ * available.
  *
  * @since 2.9
  */
@@ -76,7 +80,11 @@ public void deserializeAndSet(JsonParser p, DeserializationContext ctxt,
             newValue = delegate.deserializeWith(p, ctxt, oldValue);
         }
         if (newValue != oldValue) {
-            delegate.set(instance, newValue);
+            // 31-Oct-2016, tatu: Basically should just ignore as null can't really
+            //    contribute to merging.
+            if (newValue != null) {
+                delegate.set(instance, newValue);
+            }
         }
     }
 
@@ -97,20 +105,31 @@ public Object deserializeSetAndReturn(JsonParser p,
         //    try calling setter on builder? Presumably should not be required,
         //    but may need to revise
         if (newValue != oldValue) {
-            return delegate.setAndReturn(instance, newValue);
+            // 31-Oct-2016, tatu: Basically should just ignore as null can't really
+            //    contribute to merging.
+            if (newValue != null) {
+                return delegate.setAndReturn(instance, newValue);
+            }
         }
         return instance;
     }
 
     @Override
     public void set(Object instance, Object value) throws IOException {
-        delegate.set(instance, value);
+        // 31-Oct-2016, tatu: Basically should just ignore as null can't really
+        //    contribute to merging.
+        if (value != null) {
+            delegate.set(instance, value);
+        }
     }
 
     @Override
-    public Object setAndReturn(Object instance, Object value)
-            throws IOException
-    {
-        return delegate.setAndReturn(instance, value);
+    public Object setAndReturn(Object instance, Object value) throws IOException {
+        // 31-Oct-2016, tatu: Basically should just ignore as null can't really
+        //    contribute to merging.
+        if (value != null) {
+            return delegate.setAndReturn(instance, value);
+        }
+        return instance;
     }
 }

src/main/java/com/fasterxml/jackson/databind/deser/impl/SetterlessProperty.java

@@ -145,6 +145,6 @@ public final void set(Object instance, Object value) throws IOException {
     public Object setAndReturn(Object instance, Object value) throws IOException
     {
         set(instance, value);
-        return null;
+        return instance;
     }
 }

src/test/java/com/fasterxml/jackson/failing/MergeWithNullTest.java renamed to src/test/java/com/fasterxml/jackson/databind/deser/merge/MergeWithNullTest.java

@@ -1,4 +1,4 @@
-package com.fasterxml.jackson.failing;
+package com.fasterxml.jackson.databind.deser.merge;
 
 import com.fasterxml.jackson.annotation.JsonSetter;
 import com.fasterxml.jackson.annotation.OptBoolean;
@@ -19,6 +19,14 @@ public Config(int a, int b) {
         }
     }
 
+    // another variant where all we got is a getter
+    static class NoSetterConfig {
+        AB _value = new AB(2, 3);
+
+        @JsonSetter(merge=OptBoolean.TRUE)
+        public AB getValue() { return _value; }
+    }
+
     static class AB {
         public int a;
         public int b;
@@ -29,7 +37,7 @@ public AB(int a0, int b0) {
             b = b0;
         }
     }
-    
+
     private final ObjectMapper MAPPER = new ObjectMapper()
             // 26-Oct-2016, tatu: Make sure we'll report merge problems by default
             .disable(MapperFeature.IGNORE_MERGE_FOR_UNMERGEABLE)
@@ -44,6 +52,15 @@ public void testBeanMergingWithNull() throws Exception
         assertEquals(5, config.loc.a);
         assertEquals(7, config.loc.b);
     }
-    
 
+    public void testSetterlessMergingWithNull() throws Exception
+    {
+        NoSetterConfig input = new NoSetterConfig();
+        NoSetterConfig result = MAPPER.readerForUpdating(input)
+                .readValue(aposToQuotes("{'value':null}"));
+        assertNotNull(result.getValue());
+        assertEquals(2, result.getValue().a);
+        assertEquals(3, result.getValue().b);
+        assertSame(input, result);
+    }
 }