Notice: Trying to access array offset on value of type null in _field_write_instance()

Notice that Trying to access array offset on value of type null means, for example, accessing $formatter_type['module'] when $formatter_type is NULL.
I am not sure that setting $display['module'] to an empty string is much helpful, in that case. It could be helpful if it were be possible to set $display['module'] to a default module name, for example, for which invoking a hook would be later possible.

#5 does not work for me.

Still receiving the error on both remote production and dev server.

Warning: Trying to access array offset on value of type null in ctools_context_handler_get_render_handler() (line 68 of /home/.../sites/all/modules/ctools/includes/context-task-handler.inc).

Drupal 7.101
PHP 8.1.28

@frazac Not sure your warning is caused by the Drupal core, as it is in the ctools module. You can check a similar issue here: #1244434: Notice: Undefined index: handler type in ctools_context_handler_get_render_handler() (line 67 → , maybe it could help.

I think the patch is just hiding a bigger issue.
Why is $formatter_type NULL? If it is NULL, does continuing as nothing happened make sense?

As a side note, the line containing $display['module'] = $formatter_type['module']; is line 648, now.

Let's try to understand what exactly happens that makes $formatter_type set to NULL (or not initialized to a correct value).

The code containing the line causing that warning is the following one.

$display += array(
  'label' => 'above',
  'type' => isset($field_type['default_formatter']) ? $field_type['default_formatter'] : 'hidden',
  'settings' => array(),
);
if ($display['type'] != 'hidden') {
  $formatter_type = field_info_formatter_types($display['type']);
  $display['module'] = $formatter_type['module'];
  $display['settings'] += field_info_formatter_settings($display['type']);
}

$formatter_type can be NULL because field_info_formatter_types() did not find information about the $field_type['default_formatter'] formatter or the cache used by _field_info_collate_types() got corrupted. In the case $field_type['default_formatter'] is an empty string, field_info_formatter_types() would return an array with information about all the formatters (and probably cause other issues).

I changed the code to the following one.

    if ($display['type'] != 'hidden') {
      $formatter_type = field_info_formatter_types($display['type']);
      if ($formatter_type) {
        $display['module'] = $formatter_type['module'];
        $display['settings'] += field_info_formatter_settings($display['type']);
      }
    }

The reason is that:

• If the formatter has not been found, we do not know which module implements it. Leaving $formatter_type['module'] not set is probably the more correct way to say that.
• If the formatter has not been found, field_info_formatter_settings() returns an empty array. Executing $display['settings'] += field_info_formatter_settings($display['type']); is perfectly useless, since $display['settings'] has been already initialized to an empty array.