Don't add a parameter to the tag payload when its value is undefined

[googleanalyticsresoneo]

If you happen to add the email address parameter on a tag for example, but in some cases that value is undefined, the Hit will not be processed at all by Criteo's back end, resulting in data collection loss for those Events, which is sad and unexpected.

Please make sure that the Hit being built is parseable by Criteo in the backend.

For example, don't add the parameter if the value is missing / undefined.