Drupal 8.x

Hello everyone!

    I am an amateur developer, and primarily use WordPress for my clients. Wordpress has become boring, and I am looking for more of a challenge, and I have also taken on a pretty intense project. I am not sure really what to use to build it. I am familiar with all front-end languages, but this project will require an intense back-end as well. Let me know if you think Drupal would be able to help out in anyway with this!

A website for an association/network of providers. 

Will have the ability to sell a consumer membership and a provider membership

I am running Drupal 8.4.2. multi site and on one site :
We are getting the following error when we go to our website /user/login page

“The website encountered an unexpected error. Please try again later.”

We have the Drupal admin open on another system and we have the following in the reports status.
Mismatched entity and/or field definitions
The following changes were detected in the entity type and field definitions.
Content : The node.field_contact field needs to be updated.

Hi,

I need a hint as my site is down : 'https://www.77beauval.net/'

Basically it states unexpected issue. Try later.

No recent updates of modules or whatsover have been done. It just poped up today. As far as I can be sure, no server update from my hosting company neither.

If I go to ./admin/reports/dblog I see following :

If a number display field is set with setRequired(TRUE) and is not filled out NumberWidget::errorElement returns NULL which results in drupal_set_message(NULL) and ajax error at the UI.

NumberWidget

public function errorElement(array $element, ConstraintViolationInterface $violation, array $form, FormStateInterface $form_state) { return $element['value']; }

As opposed to WidgetBase:

I'm working with custom entities and I would like to add a new field which would be required (not null) in the database but not required at the UI. The reason for not required at the UI is that some roles doesn't have the option to fill out. In these cases the field is populated automatically in the overriden ContentEntityForm:save method.

At the entity class:

Could anyone please help me on Drupal 8 migration from URL.

The source is a URL which is returning JSON data without any authentication & I chosen Drupal 'entity:node' as destination.

Please see below the migration script I've written, the script seems correct to me as per Drupal 8 migration standard, not sure if I am missing something.

migrate_plus.migration_group.icf_taleo.yml