Select::extractValue

static function extractValue(FieldType $fieldType, array $field, array $request)
{
	$value = parent::extractValue($fieldType, $field, $request);
	$value =
		!empty(static::getFieldOptions($fieldType))
			? self::validateValueSingle($value, $fieldType)
			: null
	;

	$errors = static::getErrors();
	if (!empty($errors) && $value === null)
	{
		$lastErrorKey = array_key_last($errors);
		if (!array_key_exists('parameter', $errors[$lastErrorKey]))
		{
			$errors[$lastErrorKey]['parameter'] = static::generateControlName($field);
		}

		static::cleanErrors();
		static::addErrors($errors);
	}

	return $value;
}