Unfix #357; should help with other problems like JAXB module issue 54 (FasterXML/jackson-module-jaxb-annotations#54)

Author: cowtowncoder

src/main/java/com/fasterxml/jackson/databind/cfg/ContextAttributes.java

@@ -177,12 +177,14 @@ public ContextAttributes withPerCallAttribute(Object key, Object value)
                 // need to mask nulls to ensure default values won't be showing
                 if (_shared.containsKey(key)) {
                     value = NULL_SURROGATE;
-                } else {
+                } else if ((_nonShared == null) || !_nonShared.containsKey(key)) {
                     // except if non-mutable shared list has no entry, we don't care
                     return this;
+                } else {
+                    _nonShared.remove(key);
+                    return this;
                 }
             }
-
             // a special case: create non-shared instance if need be
             if (_nonShared == null) {
                 return nonSharedInstance(key, value);

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

@@ -394,9 +394,11 @@ protected JsonSerializer<?> findConvertingContentSerializer(SerializerProvider p
          */
         Object ob = provider.getAttribute(CONVERTING_CONTENT_CONVERTER_LOCK);
         if (ob != null) {
-            return existingSerializer;
+            if (ob == Boolean.TRUE) { // just to ensure it's value we added.
+                return existingSerializer;
+            }
         }
-        
+
         final AnnotationIntrospector intr = provider.getAnnotationIntrospector();
         if (intr != null && prop != null) {
             AnnotatedMember m = prop.getMember();

src/test/java/com/fasterxml/jackson/databind/convert/TestConvertingSerializer.java

@@ -218,10 +218,4 @@ public void testIssue731() throws Exception
         // must be  {"a":2,"b":4}
         assertEquals("{\"a\":2,\"b\":4}", json);
     }
-
-    // [databind#357]
-    public void testConverterForList357() throws Exception {
-        String json = objectWriter().writeValueAsString(new ListWrapper());
-        assertEquals("{\"list\":[[\"Hello world!\"]]}", json);
-    }
 }

src/test/java/com/fasterxml/jackson/failing/TestConvertingSerializer357.java

@@ -0,0 +1,38 @@
+package com.fasterxml.jackson.failing;
+
+import java.util.*;
+
+import com.fasterxml.jackson.databind.annotation.JsonSerialize;
+
+import com.fasterxml.jackson.databind.util.StdConverter;
+
+public class TestConvertingSerializer357
+    extends com.fasterxml.jackson.databind.BaseMapTest
+{
+    // [databind#357]
+    static class Value { }
+
+    static class ListWrapper {
+        @JsonSerialize(contentConverter = ValueToStringListConverter.class)
+        public List<Value> list = Arrays.asList(new Value());
+    }
+
+    static class ValueToStringListConverter extends StdConverter<Value, List<String>> {
+        @Override
+        public List<String> convert(Value value) {
+            return Arrays.asList("Hello world!");
+        }
+    }
+
+    /*
+    /**********************************************************
+    /* Test methods
+    /**********************************************************
+     */
+
+    // [databind#357]
+    public void testConverterForList357() throws Exception {
+        String json = objectWriter().writeValueAsString(new ListWrapper());
+        assertEquals("{\"list\":[[\"Hello world!\"]]}", json);
+    }
+}