What are the variables DUMMY_GROOVY_SOURCE and DUMMY_GROOVY_TRGT assigned to in your script? How about Oracle, is this assigned to the correct Model code? I think some more of your code would provide a better context for determining the cause of the error.
You can always debug using out.print, as follows:
This will allow you to determine if objects are being set correctly in the code.
interactiveHelper.performAction(new InterfaceActionAddSourceDataStore(odiDatastore1, dataSet, new AliasComputerDoubleChecker(), new ClauseImporterLazy(), new AutoMappingComputerLazy()));
interactiveHelper.performAction(new InterfaceActionSetTargetDataStore(targetDatastore, new MappingMatchPolicyLazy(), new AutoMappingComputerLazy(), new AutoMappingComputerLazy(), new TargetKeyChooserPrimaryKey()));
Groovy version - Getting Groovy with ODI
Extending the interface accelerator example (auto mapping extensions);
More interface accelerator options around auto mapping;
Interface Builder (explicit interface definition driven from a file);
I agree with David. Take a look at all of the other resources available. Plus, you can use the process I mentioned to print out the object value for debugging to ensure the text file is being read correctly.
Unfortunately, without having your full environment in front of me it's tough to offer you further advice.