Service/CustomFieldsHelper.php
public function getCustomField($class, $slug = null)
    {
        if (!$slug) {
            throw CustomFieldsHelperException::slugIsMissing();
        }
        
        $resolveClass = (is_string($class)) ? $class : get_class($class);
        if (!$this->cache[$resolveClass][$slug]) {
            $this->_cacheCustomFields($resolveClass);
        }
        
        return $this->cache[$resolveClass][$slug];
    }
public function getCustomField($class, $slug = null)
    {
        if (!$slug) {
            throw CustomFieldsHelperException::slugIsMissing();
        }
        
        $resolveClass = (is_string($class)) ? $class : get_class($class);
        if (!$this->cache[$resolveClass][$slug]) {
            $this->_cacheCustomFields($resolveClass);
        }
        
        return $this->cache[$resolveClass][$slug];
    }
Return a requested customField

@param object|string $class The requested class
@param string $slug The slug. BEWARE If the slug is null, throw a proper CustomFieldsHelperException
@return CustomField The requested CustomField
@throws CustomFieldsHelperException if $slug is null