SQLite3 can only bind numbers, strings, Buffers and null at Post.save
Your issue is as I suppose connected with fact that you have did some manual work in the database. In the post table for the “template” column you have null values instead of empty strings. This leads to the problem.
Do you appreciate the support you've received today? If so, consider donating to the Publii team by clicking here; we'll be sure to use your donation to make Publii even better!