fix

vlib/v/markused/walker.v

@@ -1183,6 +1183,9 @@ pub fn (mut w Walker) mark_by_sym(isym ast.TypeSymbol) {
 			w.mark_by_type(isym.info.key_type)
 			w.mark_by_type(isym.info.value_type)
 			w.features.used_maps++
+			if isym.info.value_type.has_flag(.option) {
+				w.used_option++
+			}
 		}
 		ast.Alias {
 			w.mark_by_type(isym.info.parent_type)

vlib/v/tests/options/option_map_val_test.v

@@ -0,0 +1,6 @@
+fn test_main() {
+	mut m := map[int]?u32{}
+	if c := m[0] {
+		println('c:  ${c} not none!')
+	}
+}