For backwards compatibility some internal clients were sending requests to the multipart endpoint but not sending an attachment field. This worked on the 2.3.x line but on 2.5.x it is enforced more strictly and is throwing 400. The proper thing to do would be to make the clients do the right thing but it would be such a long tail that releasing this fix is more effective short term while that logic is slowly phased out.
Coverage remained the same at 93.781% when pulling c6ffbc6e68280f4f5ba0270c4f9a1ecbaccfeac3 on tgianos:optionalAttachmentsDev into 6d176f18c5f58b8da9e8742985173437ae69e004 on Netflix:master.
For backwards compatibility some internal clients were sending requests to the multipart endpoint but not sending an attachment field. This worked on the 2.3.x line but on 2.5.x it is enforced more strictly and is throwing 400. The proper thing to do would be to make the clients do the right thing but it would be such a long tail that releasing this fix is more effective short term while that logic is slowly phased out.