Ignore exception cause when it's not another exception

[pedro]

Custom error classes might define #cause as a string or similar, which would in turn result in an internal Rollbar error.

[jondeandres]

@pedro do you have this error using third party libraries? the problem is with some custom exceptions of your own?

I remember we had a problem with another library that defined its own #cause method, but upgrading the library resolved the problem.

Can you give us those details?

Thanks

[pedro]

Hey! For sure, it is actually a private library, so we'll probably end up changing the method name.

But seeing that Ruby didn't give us any warning when we defined that method, and that debugging this in Rollbar took quite some time, I figured it might be worth being extra cautious here. Searching in Github this method doesn't seem all uncommon (wish there was a way to skip duplicates heh).