com.google.api.client.http.MultipartContent class by default uses constant '__END_OF_PART__' string as the boundary (part delimiter).
It will cause problem if the data to be transfered includes this string. Such problems could be really hard to investigate.
Example of such problem:
googleapis/google-cloud-java#6386

The class also provides setBoundary(String) method to alter the default boundary, but this method is not accessible from the other project.