[TYPO3-mvc] Debugging repository: The method "id2name" is not supported

[Wild Axel]

Hello,

I'm debugging my Typo3 extension. Typo3 is running on a Ubuntu 14.04 server. I'm remote debugging with NetBeans on a Windows host.

Case1: 
if I'm debugging my method  findBySport in my ABCRepository (extends \TYPO3\CMS\Extbase\Persistence\Repository) WITHOUT using any breakpoints, everything works fine.
   
    public function findBySport($sportID){
        $query = $this->createQuery();
        $query->matching($query->equals('sport', $sportID));        
        return $query->execute();        
    }

Case 2:
if I'm debugging this method WITH a breakpoint, I will get this error:

#1233180480: The method "id2name" is not supported by the repository. (More information)
TYPO3\CMS\Extbase\Persistence\Generic\Exception\UnsupportedMethodException thrown in file
/usr/share/typo3/typo3_src-6.2.11/typo3/sysext/extbase/Classes/Persistence/Repository.php in line 293.

CASE3:
After implementing an empty id2name-method in my ABCRepository I'm able to debug with using breakpoints without any errors.
public function id2name(){ }

Could someone explain to me what's going on here? Regards, Axel