i get error at step 4 in ub data migration in m2

……………………………………………………………………………………………………..PHP Error[2]: Creating default object from empty value
in file /var/www/vhosts/commgeardelta.99stockpics.com/httpdocs/pub/ub-tool/protected/controllers/Step4Controller.php at line 252
#0 /var/www/vhosts/commgeardelta.99stockpics.com/httpdocs/pub/ub-tool/protected/controllers/Step4Controller.php(125): Step4Controller->_migrateCatalogCategories()
#1 /var/www/vhosts/commgeardelta.99stockpics.com/httpdocs/pub/ub-tool/protected/commands/RunCommand.php(58): Step4Controller->actionRun()
#2 /var/www/vhosts/commgeardelta.99stockpics.com/httpdocs/pub/ub-tool/protected/commands/RunCommand.php(28): RunCommand->_migrateData()
#3 unknown(0): RunCommand->actionIndex()
#4 /var/www/vhosts/commgeardelta.99stockpics.com/httpdocs/pub/ub-tool/yii-1.1.19/console/CConsoleCommand.php(172): ReflectionMethod->invokeArgs()
#5 /var/www/vhosts/commgeardelta.99stockpics.com/httpdocs/pub/ub-tool/yii-1.1.19/console/CConsoleCommandRunner.php(71): RunCommand->run()
#6 /var/www/vhosts/commgeardelta.99stockpics.com/httpdocs/pub/ub-tool/yii-1.1.19/console/CConsoleApplication.php(92): CConsoleCommandRunner->run()
#7 /var/www/vhosts/commgeardelta.99stockpics.com/httpdocs/pub/ub-tool/yii-1.1.19/base/CApplication.php(185): CConsoleApplication->processRequest()
#8 /var/www/vhosts/commgeardelta.99stockpics.com/httpdocs/pub/ub-tool/yii-1.1.19/yiic.php(33): CConsoleApplication->run()
#9 /var/www/vhosts/commgeardelta.99stockpics.com/httpdocs/pub/ub-tool/protected/ubdatamigration_cli.php(5): require_once()
#10 /var/www/vhosts/commgeardelta.99stockpics.com/httpdocs/bin/ubdatamigration(4): require_once()