MongoSpark cast ISODate object

Question

I am trying to read a collection from mongo using MongoSpark with a timestamp field called TimeInstant:

I have a problem with this timestamp type field. It seems that some of the values of this field in the collection are with a empty String, so mongo infers this field for me as a string. The problem is that instead of returning a String with the timestamp, it returns an object that looks like this:

The problem is that when I try to cast this field to TimestampType it returns null values. My question is how can I cast this $date object to timestamp. I have tried to increase the number of samples when reading from mongo but it keeps inferring this field as a string