Filed as a follow-up to issue 135148. Once you create a BPEL process, the error message on the empty sequence says: 

"The content of element 'sequence' is not complete. One of documentation, targets, sources, assign, compensate,
compensateScope, empty, exit, extensionActivity, flow, forEach, if, invoke, pick, receive, repeatUntil, reply, rethrow,
scope, sequence, throw, validate, wait, while is expected."

While this is much better than it was before (135148), the list of 24 (!) element names is still unlikely to be
correctly perceived by a human being. I would expect the error message to read: "The content of the <sequence> activity
is not complete. A <sequence> must contain at least one child activity." Moreover, the current error message is
misleading, as it says that adding <documentation> is enough to fix the error, while it is not.