nitc: accepts 'var x = null'

Signed-off-by: Jean Privat <jean@pryen.org>
nitg&i: accepts 'var x = null'

Signed-off-by: Jean Privat <jean@pryen.org>
tests: add base_var_null2

Signed-off-by: Jean Privat <jean@pryen.org>
Merge branch 'var_null'