[JIRA issue processing] Unassigning users leads to multitude of empty users

[bockthom]

Description

In the JIRA issue data, there can be "assigned" events if a user assigns another user to this issue.
However, there are no "unassigned" events (in contrast to GitHub issue data). Instead, in the JIRA issue data, "unassigend" events are represented by "assigned" events where the target ("event_info_1" and "event_info_2") is the empty user "".
This can be problematic, as a new e-mail address is generated for each of these "unassign" events and then we have a multitude of empty users added to the author data and also appearing in the issue data which are actually no users.

Ideas on how to solve this problem

(1) Fix this within the JIRA issue processing to directly represent "unassigned" events in a similar way than for GitHub issue data. (However, this would affect all the already processed JIRA issue data...)

(2) Add an additional wrapper script which handles this or directly fix this in the author postprocessing to remove multiple occurrenes of the empty user having different e-mail addresses...