Need clearer error message when you try to dereference Properties on a primitive Type

Summary: I've been working on formatting the Stray Bullets Timeline page, relying heavily on _groupBy. However, some QL code I came up with (in Event) for displaying Time with a colon in the middle strangely doesn't work when nested inside _groupElements. At least, that's what I suspect the culprit is.

Check out page https://www.querki.net/u/AlexxKay/stray-bullets/#!.7w4g85n When line 14 is replaced with just [[Time]] It evaluates correctly. But as is, I'm getting some sort of type mismatch error?

Later: see comments below. The actual problem is that the page was dereferencing the "Time" Property on a Whole Number, which is just plain illegal. But the error message was utterly cryptic in this circumstance. We should come up with a better one -- at the least, trying to apply a Property to a non-Thing should probably produce an explicit error to that effect...