.../sqldeveloper/sqldeveloper/extensions/oracle.sqldeveloper.migration.mysql.jarfile, and look for
/oracle/dbtools/migration/workbench/plugin/mysql/MySQLDefaultValuesMappingRules.xmlyou will see it inside there.
Otherwise you might try verifying that all your NLS settings are consistent, both for Migration and the Database. That is:
AddVMOption -Duser.language=en AddVMOption -Duser.country=US
This is not my area of expertise. I think some settings depend whether your migration is on- or off-line. If nothing mentioned here works for you, just post again on this thread and perhaps someone more knowledgeable will respond.
Tools > Preferences > Database > NLS Tools > Preferences > Migration > Data Move Options (either Masks or the User-Defined Custom Preferences By Source Type) Tools > Preferences > Migration > Translators