Unable to download collector map for offline use - "Parameters cannot be null"

[ShaneKrupimpski]

Hey there - new to collector and webmaps in general. Currently attempting to download a collector map for offline use and failing. I have gone over all my layers and have edited any custom fields to allow null values to no avail. I have roughly 10 empty hosted feature layers and a vektor tile basemap. Just curious if this is a common problem or if there is something I'm missing. If any more info is needed just ask. Currently on Samsung Galaxy Tab Active 2 android version 8.1.0

Thanks a  bunch

EDIT: Changed basemap to a tpk and am now recieving error message: attempt to invoke virtual method 'java.lang.string java.lang.string.toLowerCase(java.util.Locale)' on a null object reference 

[CBMTDatamanager]

I have the same problem. I've searched and tried all sorts of modifications with no luck.

[MiaogengZhang · Accepted solution]

Current Android market version of Collector doesn't support vector basemap. If you try to download, you will see an error "parameters cannot be null". Can you try using imagery basemap and see if the issue still happens?