Problem Description:
When I try to create an attachement for a process instance and do not provide a task id, then an exception is thrown.

Expected behavior:
I can create an attachment for a process instance without a task id.

Hint

org.camunda.bpm.engine.impl.cmd.CreateAttachmentCmd#execute

ensureNotNull("taskId", taskId);

and the line before the last line

commandContext.getOperationLogManager().logAttachmentOperation(UserOperationLogEntry.OPERATION_TYPE_ADD_ATTACHMENT, task, propertyChange);

are only places where taskId is forced