Issue Summary

This is reproducible on Data Center: (yes)

Implementing PreMigrationCheckRepository and returning a CSV, for example with

CheckResultBuilder builder = resultBuilder(WARNING).withCsvFileContent(csvFile);
return builder.build();

will cause JCMA to throw an error when trying to download the CSV file through the user interface.
 

Steps to Reproduce

1. Run a JCMA migration with an app that implements vendor pre-checks that will fail with a warning
2. Click on Download Report in JCMA

Expected Results

A CSV file is downloaded

Actual Results

The below exception is thrown in the browser with XML formatting (nothing in the logs)

com.atlassian.jira.migration.preflight.csv.UnableToWriteCsvException: Csv content is empty
	at com.atlassian.jira.migration.preflight.rest.PreflightResource.generateAppVendorCheckCSV(PreflightResource.kt:186)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available