only attempt to convert and add push token if present (#756)
only attempt to convert and add push token if present (#756)

* only convert token to string if token present

* convert token and then check for non nil value

mixpanel/mixpanel-iphone,mixpanel/mixpanel-iphone,mixpanel/mixpanel-iphone,mixpanel/mixpanel-iphone,mixpanel/mixpanel-iphone