fix panic based error reporting
diff --git a/query.go b/query.go
index a02af99..f32bf2e 100644
--- a/query.go
+++ b/query.go
@@ -70,6 +70,7 @@
 	}
 }
 
+// Query queries q in g.
 func Query(w io.Writer, q string, g *DepGraph) {
 	if q == "$MAKEFILE_LIST" {
 		for _, mk := range g.accessedMks {