Oh! I fix it. I've opened the file.m with TextEdit. Then I browse to: File > Revert To> Browse All Versions
It led me to a place with all saved versions of the file, where I could search with a timeline the exact moment I need.
I've find the version previous to the blank/crash moment, and copied the text, paste it at file.m on xcode( also saved, commit it to source control for safety) and everything is ok now. I could recover all my code again.