How does one submit files through a SuiteScript 2.0 Suitelet?

I'm having issues with serverWidget.FieldType.FILE. I need to be able to submit a file with a form from a Suitelet, and I seem to be at a dead end. Has anyone else figured out how to do this in SuiteScript 2.0 yet? Any help is appreciated.

If I do this...

 form.addField({      id: 'custom_file',      type: serverWidget.FieldType.FILE,      label: 'File Upload'  });

...I get the expected file input, but upon submitting the form, context.request.parameters.custom_file is undefined. Of course, if I do this instead...

 form.addField({      id: 'custom_text',      type: serverWidget.FieldType.TEXTAREA,      label: 'Text Area'  });