Requesting workspaces endpoint without a header leads to 500

[Omeramsc]

When calling the workspaces endpoint (either with a specific workspace or for all workspaces) without the X-Email header, the server will respond with 500 Internal server error.

This is not desirable and should be fixed, either with an empty response, null workspace (as being returned when there are no workspace for a certain user), or with a readable error.

*This change should be followed with a change in the tests as well.