SCSS: This variable was not declared

[rhoudroge]

This is about Bulma.

Overview of the problem

This is about the Bulma CSS framework and compiling an SCSS file that used to work with v0.9

Description

Hi!
Thanks for the great work maintaining Bulma! I've been very happy using this framework.
I am upgrading from 0.9 to 1.0, and it seems some customisation variables have disappeared, such as $navbar-item-color with SASS now showing this error: Error: This variable was not declared with !default in the @used module.
Could you please let me know how to deal with these variables, I have a number of them in my source file?
Thanks!

Steps to Reproduce

1. Define the above variable in the scss file when importing navbar using the with directive
2. Compile the SCSS file

Expected behavior

SCSS compiles correctly

Actual behavior

The actual compilation results in the above error.