Steps to reproduce
1. Installed the module using Composer with the command: composer require 'drupal/webicons:^1.0'.
2: when we try to add a new field inside of content types it throws a warning, warnings mentioned below.
Warning: Undefined array key "field_webicons" in Drupal\webicons\Plugin\Field\FieldWidget\WebIconsFieldWidget->formElement() (line 80 of modules\contrib\webicons\src\Plugin\Field\FieldWidget\WebIconsFieldWidget.php).
Warning: Trying to access array offset on null in Drupal\webicons\Plugin\Field\FieldWidget\WebIconsFieldWidget->formElement() (line 96 of modules\contrib\webicons\src\Plugin\Field\FieldWidget\WebIconsFieldWidget.php).
Warning: Trying to access array offset on null in Drupal\webicons\Plugin\Field\FieldWidget\WebIconsFieldWidget->formElement() (line 96 of modules\contrib\webicons\src\Plugin\Field\FieldWidget\WebIconsFieldWidget.php).
Warning: Trying to access array offset on null in Drupal\webicons\Plugin\Field\FieldWidget\WebIconsFieldWidget->formElement() (line 96 of modules\contrib\webicons\src\Plugin\Field\FieldWidget\WebIconsFieldWidget.php).
Warning: Trying to access array offset on null in Drupal\webicons\Plugin\Field\FieldWidget\WebIconsFieldWidget->formElement() (line 105 of modules\contrib\webicons\src\Plugin\Field\FieldWidget\WebIconsFieldWidget.php).
Warning: Trying to access array offset on null in Drupal\webicons\Plugin\Field\FieldWidget\WebIconsFieldWidget->formElement() (line 105 of modules\contrib\webicons\src\Plugin\Field\FieldWidget\WebIconsFieldWidget.php).
Warning: Trying to access array offset on null in Drupal\webicons\Plugin\Field\FieldWidget\WebIconsFieldWidget->formElement() (line 105 of modules\contrib\webicons\src\Plugin\Field\FieldWidget\WebIconsFieldWidget.php).
Warning: Trying to access array offset on null in Drupal\webicons\Plugin\Field\FieldWidget\WebIconsFieldWidget->formElement() (line 122 of modules\contrib\webicons\src\Plugin\Field\FieldWidget\WebIconsFieldWidget.php).
Warning: Trying to access array offset on null in Drupal\webicons\Plugin\Field\FieldWidget\WebIconsFieldWidget->formElement() (line 122 of modules\contrib\webicons\src\Plugin\Field\FieldWidget\WebIconsFieldWidget.php).
I've attached image illustrating my actions—installing the module and searching within the extend panel.