Hi, I recently posted about putting together a parts caster. Today I was sanding a contour into the body and after taking some material out the grain became like this, I am not sure how to describe it so I couldn't get any results when searching It appears to be hollow inside, I can't say for sure if it is an air pocket or it is chambered or what. I am not sure of the specifics of this body as I bought it used, but it is by "Holy Grail Guitars Co.". I'm not sure of what action to take here, two things i have thought of is just 1. filling it with sawdust and superglue, or 2. Using wood filler, and then just a quick final sanding to finish it off and go no further. Could anyone else give me some pointers or possible fixes for this?