e-notice in survey correctly identifies orphan variable - expect some functional impact dunno what

I get

Undefined variable: customFieldID Notice Survey.php 898 CRM_Campaign_BAO_Survey::getSurveyResponseFields()

when I look at the line I see

$customValue = CRM_Utils_Array::value( $customFieldID, $customFields );

$customFieldID is not defined anywhere that I can see so this probably points to something not working as it should