magento2 – The LESS Grunt compile fails with an error when compiling lib / web / css / docs / source / docs.less

I hope to get some advice. I took out a project that I had not touched in a long time and in developer mode I ran & # 39; grunt exec & # 39; followed by & # 39; grunt less & # 39; and once running & # 39; grunt less & # 39; I received the following error. Magento 2.2.6

Running the "less: documents" (less) task

NameError: .lib-url-check is not defined in lib / web / css / docs / source / _utilities.less in line 402, column 5:
401 // "Call" the mixin
402 .lib-url-check (@_ icon-image);
403 Warning: Error compiling lib / web / css / docs / source / docs.less Use –force to continue.

Aborted by warnings.

The code for around line 401:

.example-url-check-false {
// Set the path to use the image in false
@ _icon-image: false;

// "Call" the mixin
.lib-url-check (@_ icon-image);

// will return & # 39; false & # 39; and it does not generate anything
.lib-css (background, #eee @ lib-url-check-output non-repetition 0 0);
}

This file is an unmodified central file, how do I debug the cause of this problem / resolution?

I would appreciate any help you may receive.

Thank you!