Strange __NSCFString error

Question

I have been getting some reports with this error:

-[__NSCFString replaceOccurrencesOfString:withString:options:range:]: nil argument

I have search in my code for this method, but I am not using it all. My assumption is that another method internally uses replaceOccurrencesOfString:withString:options:range:. Am I correct? Which methods could be responsible for this?

Note that I cannot provide a full stack trace as this error happens inside an exception handler. I am also unable to reproduce this issue.