What did you do to get to this? Are there any steps to reproduce it?

I think I can see the source of it but don't know yet how to reproduce it.

I did nothing, just install a fresh Joomla 3.7 without any custom field created.
The foreach gets a non-array so there is the warning.

As a side note there is even this issue

Did you use latest staging (or the alpha1) to create that installation and created a fresh database for it? Because the field should have been created with that SQL: https://github.com/joomla/joomla-cms/blob/staging/installation/sql/mysql/joomla.sql#L643

I've tried deleting all entries in all fields related tables and can't reproduce this error.

I did nothing, just install a fresh Joomla 3.7 without any custom field created.

hmm i have a alpha1 here and i can't reproduce this too. Can you please double check that on a clean installation with a clean database too. As we are allowed to do breaking chnages between dev and alpha versions etc ;)

Also can you tell us which page do you visite on the frist screenshot? The single article view or something different?

@joeforjoomla can't get your Issue. Is issue on latest staging too?

I'm closing this for now since nobody seems to be able to reproduce it. Feel free to reopen if it's still an issue with latest staging.