The best part about these errors is that you actually get exactly what’s wrong with it :-)
The java code uses a deprecated method (getType()) – see documentation: https://apidocs.rnd.mendix.com/8/runtime/com/mendix/systemwideinterfaces/core/meta/IDataValidation.html
As you can see in the version 9 documentation, getType doesn’t exist anymore: https://apidocs.rnd.mendix.com/9/runtime/com/mendix/systemwideinterfaces/core/meta/IDataValidation.html
So simply change getType into getValidationType in \javasource\migrationtoolkit\impl\AttributeAnalyser.java on line 54 and you’re done.