Allow NULL parameter values in Zend/Json/Server

Allow NULL as an acceptable value for non-optional method parameters.
Added test case
Fixed formatting issue
Merge branch 'master' of git://github.com/djskinner/zf2 into hotfix/3767
[#3767] CS fixes

- indentation, trailing_spaces
Merge branch 'hotfix/3767'

Close #3767
Fixes #3696
Fixes #2752