Well here’s an error log:
Parameters: {"theme"=>#<ActionDispatch::Http::UploadedFile:0x00007fc32bc88958 @tempfile=#<Tempfile:/tmp/RackMultipart20171103-338-1gjeut6.json>, @original_filename="mrf-tweaks.dcstyle.json", @content_type="application/json", @headers="Content-Disposition: form-data; name=\"theme\"; filename=\"mrf-tweaks.dcstyle.json\"\r\nContent-Type: application/json\r\n">}
Completed 500 Internal Server Error in 4ms (ActiveRecord: 0.5ms)
RuntimeError (Unknown type passed to set field)
/var/www/discourse/app/models/theme.rb:253:in `set_field'
This is strange because I downloaded this file from this very same server before uploading a new import.