Revert "Merge branch 'system-not-null'"

This reverts commit 6ec0d8d2c955fbdeb1df915004b7cfc162d36606, reversing
changes made to 516c8fdb3202c87196680e400feb9ad6914c84b3.
Merge pull request #249 from church29/revert_system_not_null

Revert "Merge branch 'system-not-null'"