diff --git a/src/index.ts b/src/index.ts
index 46cd20a..4969e5b 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -356,8 +356,8 @@ class Renderer {
                 }
                 const cause = (causingTurnId !== null)
                     ? this.turnMap.get(fromJS(causingTurnId))!
-                    : null;
-                if (cause !== null) {
+                    : void 0;
+                if (cause !== void 0) {
                     this.connect(cause.point, new P.Point(swimlane.midX, this.ypos));
                 }
 
@@ -371,7 +371,7 @@ class Renderer {
                     let entryClass: string;
                     let label: string;
                     let tooltip: string = `Turn ${stringify(turn.id)} in ${swimlane.label}`;
-                    if (cause !== null) {
+                    if (cause !== void 0) {
                         tooltip += `\n  caused by ${stringify(causingTurnId!)} in ${cause.swimlane.label}`;
                     }
                     if (a._variant !== "dequeue" && a._variant !== "dequeueInternal" && triggerEvent !== null) {