Error messages are missing spaces.

[rosiel]

When a term isn't found with the desired URI, I got:

Error generating event: Could not locate derivative term with urihttps://projects.iq.harvard.edu/fits

This is an issue to add the appropriate space. I mean, it's kind of a typo, but also, "derivative term" is misleading (the term's not derivative of anything. It's for a derivative that we're trying to generate, and that's not clear.)

It might be useful to also way whether this means "No FITS derivative will be requested" or something?