Update the initial chunked attachment creation on the target to use an empty content #76
  Add this suggestion to a batch that can be applied as a single commit.
  This suggestion is invalid because no changes were made to the code.
  Suggestions cannot be applied while the pull request is closed.
  Suggestions cannot be applied while viewing a subset of changes.
  Only one suggestion per line can be applied in a batch.
  Add this suggestion to a batch that can be applied as a single commit.
  Applying suggestions on deleted lines is not supported.
  You must change the existing code in this line in order to create a valid suggestion.
  Outdated suggestions cannot be applied.
  This suggestion has been applied or marked resolved.
  Suggestions cannot be applied from pending reviews.
  Suggestions cannot be applied on multi-line comments.
  Suggestions cannot be applied while the pull request is queued to merge.
  Suggestion cannot be applied right now. Please check back later.
  
    
  
    
When running a migration recently, the work items with attachments failed to upload the attachments with the error:
Unable to upload attachment EmploymentRefsScreen_inside-app_statuses.docx for source work item 35991 to the target account. The request indicated a Content-Type of "application/x-www-form-urlencoded" for method type "POST" which is not supported. Valid content types for this method are: application/json, application/json-patch+json, application/octet-stream.. The request indicated a Content-Type of "application/x-www-form-urlencoded" for method type "POST" which is not supported. Valid content types for this method are: application/json, application/json-patch+json, application/octet-stream.I believe that there was a change to the HttpClient that sent "application/x-www-form-urlencoded" for empty content, which the Azure DevOps api was unhappy with.
This fixes that problem by adding an empty content to that first post for sending a chunked attachment.