Form Data grouped radio buttons errors

Hi,
i have an EFG form which is storing data's.
in this form i have some radio buttons and the group option is checked.

if someone is filling the form, and i want to check and edit the record in the Backend.
i have this :

Code:

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Warning: Invalid argument supplied for foreach() in system/modules/efg/drivers/DC_Formdata.php on line 1514
#0 system/modules/efg/drivers/DC_Formdata.php(1514): __error(2, 'Invalid argumen...', 'xxxxxxxxx...', 1514, Array)
#1 system/modules/core/classes/Backend.php(622): Efg\DC_Formdata->edit()
#2 system/modules/core/controllers/BackendMain.php(126): Contao\Backend->getBackendModule('fd_my-form...')
#3 contao/main.php(20): Contao\BackendMain->run()
#4 {main}

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i noticed that if i uncheck the group option for the radios buttons, (and save again the form params), error is gone.