Service/CustomFieldsHelper.php
private function getCustomFieldValue(array $fields, $class, $slug)
    {
        return (isset($fields[$slug])) ? $this->provider
            ->getCustomFieldByType($this->getCustomField($class, $slug)->getType())
            ->deserialize($fields[$slug]) 
            : null;
    }
private function getCustomFieldValue(array $fields, $class, $slug)
    {
        return (isset($fields[$slug])) ? $this->provider
            ->getCustomFieldByType($this->getCustomField($class, $slug)->getType())
            ->deserialize($fields[$slug]) 
            : null;
    }
Return the stored/raw value of a custom field.

The method return null if the slug is not recorded.

@param array $fields  the **raw** array, as stored in the db
@param object|string $class
@param string $slug
@return mixed|null The value or null if the slug is not recorded