Uplaoding an attachment for Work items

Using the RAST API.

I would like to know which URL i have to use to upload attachments which can be linked to work items.

For Test Executions in RQM i use
https://:/jazz/secure/service/com.ibm.rqm.planning.service.internal.rest.IAttachmentRestService

But those attachments are not in scope for the work items, so i cannot link them.

I already tried
https://:/jazz/secure/service/com.ibm.team.workitem.service.internal.rest.IAttachmentRestService

but i only received internal server errors (500) when trying this.

Anyone knows the correct link or has a good advice for me?


Thanks in advance,

Finaris

/edit: Another Hint, maybe the url is correct, but i saw that a NullPointer Exception occures when trying to uplaod an attachment:
http://250kb.de/u/100121/j/70pxX3uyeZYM.JPG