Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules
If not, and it's a fairly small gap in the joints, then mix some talcum powder with either clear varnish or a light grey paint. It should be the consistency of thin porridge. Just brush this into the joint lines, or use a tooth pick/cocktail stick, and let it set. Most of it will find its own level, and can be easily sanded, although you might have to repeat the application.