Rename `ExistsCheck.to_string` to reflect its intent as a debugging utility
Rename `ExistsCheck.to_string` to reflect its intent as a debugging utility

Reviewed By: dsainati1

Differential Revision: D10854252

fbshipit-source-id: da490d69de44a7eaa555e69597f0e4bb1f62a393

nmote/flow,nmote/flow,nmote/flow,nmote/flow,nmote/flow,nmote/flow,nmote/flow