SerializationGraphNavigator not receiving correct serializeNull config during initialize

[gabrielspiteri-highlight]

Q	A
Bug report?	yes
Feature request?	no
BC Break report?	yes
RFC?	no

If you set the serialize_null yaml config to true with the following configuration:

jms_serializer:
   default_context:
        serialization:
            serialize_null: true

The context object received by the SerializationGraphNavigator the shouldSerializeNull method always returns false

Steps required to reproduce the problem

1. Configure JMS to serialize_null: true
2. Serialize and object with null properties

Expected Result

• Properties with null values show

Actual Result

• Properties with null values do not show

[goetas]

see #1159