add nullable option for json visitor
add nullable option for xml visitor
add nullable option for yaml visitor
added visitors configuration to doc
move visitNull into custom handler so not breaking interface
naming/coding conventions tidy up
merge master
move xml serialize_null config into doctype_whitelist config node
merge master, use visitNull on VisitorInterface, remove null handler
remove obsolete file
merge master
Allow access to Serializer's visitors getter
prevent method call on null
test for serializing null
Merge pull request #201 from adrienbrault/patch-3

Allow access to Serializer's visitors getter
rename getSerializeNull to shouldSerializeNull
add setSerializeNull method to VisitorInterface
added setSerializeNull to Serializer
Merge branch 'nullable' of git://github.com/hashnz/JMSSerializerBundle
reverted changes to configuration