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src/main/java/com/fasterxml/jackson/databind/introspect/JacksonAnnotationIntrospector.java

@@ -1510,8 +1510,7 @@ protected TypeResolverBuilder<?> _findTypeResolver(MapperConfig<?> config,
             Annotated ann, JavaType baseType)
     {
         // since 2.16 : backporting {@link JsonTypeInfo.Value} from 3.0
-        final AnnotationIntrospector ai = config.getAnnotationIntrospector();
-        JsonTypeInfo.Value typeInfo = ai.findPolymorphicTypeInfo(config, ann);
+        JsonTypeInfo.Value typeInfo = findPolymorphicTypeInfo(config, ann);
 
         // First: maybe we have explicit type resolver?
         TypeResolverBuilder<?> b;

src/main/java/com/fasterxml/jackson/databind/jsontype/TypeResolverBuilder.java

@@ -103,16 +103,19 @@ public TypeDeserializer buildTypeDeserializer(DeserializationConfig config,
      * Initialization method that is called right after constructing
      * the builder instance, in cases where information could not be
      * passed directly (for example when instantiated for an annotation)
+     * <p>
+     * NOTE: This method will be abstract in Jackson 3.0.
      *
      * @param settings Configuration settings to apply.
      *
      * @return Resulting builder instance (usually this builder,
      *   but not necessarily)
-     *   
-     * @since 2.16
+     *
+     * @since 2.16 (backported from Jackson 3.0)
      */
-    public T init(JsonTypeInfo.Value settings, TypeIdResolver res);
-
+    default T init(JsonTypeInfo.Value settings, TypeIdResolver res) {
+        return init(settings.getIdType(), res);
+    }
 
     /*
     /**********************************************************

src/test/java/com/fasterxml/jackson/databind/ser/jdk/MapKeySerializationTest.java

@@ -256,7 +256,6 @@ public void testUnWrappedMapWithDefaultType() throws Exception{
         assertEquals("{\"@type\":\"HashMap\",\"xxxB\":\"bar\"}", json);
     }
 
-    // [databind#838]
     public void testUnWrappedMapWithDefaultTypeWithValue() throws Exception {
         final ObjectMapper mapper = new ObjectMapper();
         SimpleModule mod = new SimpleModule("test");