Feature request from zinittest, posted on GitHub Apr 25, 2016
customer_entity.gender column are filed with zeroes or nulls. P. S. Probably error occurs because gender data are not replaced with corresponding constant values on data preparation step (https://github.com/magento/magento2/blob/develop/app/code/Magento/CustomerImportExport/Model/Import/...), so system is trying to insert string values to DB column of integer type. I was able to import gender data with following ugly piece of code inserted before new customer check https://github.com/magento/magento2/blob/develop/app/code/Magento/CustomerImportExport/Model/Import/...:
if (false !== strpos($entityRow['gender'], 'Male')) { $entityRow['gender'] = 1; } elseif (false !== strpos($entityRow['gender'], 'Female')) { $entityRow['gender'] = 2; } else { $entityRow['gender'] = 3; }
Of course it requires more proper fix.