code: public function find(ResourceIdentifierInterface $identifier)
      {
          $record = $this->lookup($identifier);
  
          if (false === $record) {
              return false;
          }
  
          return is_object($record) ? $record : null;
      }
docs: Get the record from the identity map.
  
  @param ResourceIdentifierInterface $identifier
  @return object|bool|null
  the record, false if it is known not to exist, or null if the identity map does not have the object.