Problem with NodeJS captureException

I’m trying to add extra data on an explicit sending of an exception. The docs say that an optional param of JSON may be sent. I have:

var client = new raven.Client('');
client.captureException(err.err, {
    extra: {
        request: (err.req !== undefined) ? JSON.parse(stringify(err.req)) : '',
    	response: (err.res !== undefined) ? JSON.parse(stringify(err.res)) : '',
    	inputParams: (err.input !== undefined) ? JSON.parse(stringify(err.input)) : ''

But when done like this, no exception is sent to Sentry, but if I remove the extra param, it sends fine.

Any help would be appreciated. Thanks!

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