Post migration of content from Drupal 6 (using 8.0.4) an odd thing happened!  All the blog body field entries were empty, nothing, nada, zip, zero. After fiddling and faffing with things for a little longer than I am comfortable admitting I went to create a new blog post as a test and then noticed that of course the input formats (aka Text formats) had also been migrated.

Editing the "Filtered HTML" format that was imported threw up this:

Just in case you can't see that image, the error reads:

The filter_null filter is missing, and will be removed once this format is saved.

So yes there was an odd filter there!