Fix for failing Guava Optional test (#136)

Author: mukham12

guava/src/main/java/com/fasterxml/jackson/datatype/guava/ser/GuavaBeanSerializerModifier.java

@@ -1,9 +1,13 @@
 package com.fasterxml.jackson.datatype.guava.ser;
 
+import com.fasterxml.jackson.databind.AnnotationIntrospector;
 import com.fasterxml.jackson.databind.BeanDescription;
 import com.fasterxml.jackson.databind.SerializationConfig;
+import com.fasterxml.jackson.databind.introspect.AnnotatedMember;
 import com.fasterxml.jackson.databind.ser.BeanPropertyWriter;
 import com.fasterxml.jackson.databind.ser.BeanSerializerModifier;
+import com.fasterxml.jackson.databind.ser.impl.UnwrappingBeanPropertyWriter;
+import com.fasterxml.jackson.databind.util.NameTransformer;
 import com.google.common.base.Optional;
 
 import java.io.Serializable;
@@ -25,7 +29,15 @@ public List<BeanPropertyWriter> changeProperties(SerializationConfig config,
         for (int i = 0; i < beanProperties.size(); ++i) {
             final BeanPropertyWriter writer = beanProperties.get(i);
             if (Optional.class.isAssignableFrom(writer.getType().getRawClass())) {
-                beanProperties.set(i, new GuavaOptionalBeanPropertyWriter(writer));
+                // Since 2.17: Added to preserve UnwrappingBeanProperty name transformer.
+                if (writer instanceof UnwrappingBeanPropertyWriter) {
+                    final AnnotatedMember member = writer.getMember();
+                    final AnnotationIntrospector intr = config.getAnnotationIntrospector();
+                    final NameTransformer unwrapper = intr.findUnwrappingNameTransformer(member);
+                    beanProperties.set(i, new GuavaUnwrappingOptionalBeanPropertyWriter(writer, unwrapper));
+                } else {
+                    beanProperties.set(i, new GuavaOptionalBeanPropertyWriter(writer));
+                }
             }
         }
         return beanProperties;