Getting CS0649 warnings (value never assigned) for private serialized fields

Code (CSharp):

1.         [SerializeField] private Transform messagesParent;
2.  

Warning: Assets\Scripts\Flow\SystemsManager.cs(26,38): warning CS0649: Field 'SystemsManager.messagesParent' is never assigned to, and will always have its default value null

Didn't get this warning before upgrading to 2018.3, and now my project is full of them. They also don't make sense since these values will be set in the inspector.

 

This came up already, see:
https://forum.unity.com/threads/war...hen-field-is-marked-as-serializefield.556009/

 

Hmm, I searched for it and didn't find a thread. Weird.

Thanks!