After upgrading to Millau 11.0.2 we ran into some problems with custom field renderers.  The issue has to do with an important (documented) change in the release, but the release notes are a bit cryptic.  Basically with this version, when using a custom field renderer any empty fields will now return null rather than undefined.  This caused an issue for us as our custom field renderers have condition logic to handle empty fields based on undefined.  This impacts the second argument passed into a custom field renderer snippet.  Not difficult to fix and better behavior, but it’s an impacting change and I thought it would be good to pass along the learning.  

Here’s the item in the release notes.

• /CORE-935] - getFieldValue(s) API methods should return “null” instead of “undefined” (pre Q2 behavior)