diff --git a/.eslintrc.js b/.eslintrc.js
index a881f38..f7aac50 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -27,6 +27,13 @@ module.exports = {
                 allowNullableObject: true,
                 allowNullableBoolean: true
             }
+        ],
+        "eqeqeq": [
+            "error",
+            "always",
+            {
+                "null": "never"
+            }
         ]
     },
     globals: {
diff --git a/src/game/persistence.ts b/src/game/persistence.ts
index e760411..4e7704d 100644
--- a/src/game/persistence.ts
+++ b/src/game/persistence.ts
@@ -62,6 +62,8 @@ export type State =
     | number
     | boolean
     | DecimalSource
+    | null
+    | undefined
     | { [key: string]: State }
     | { [key: number]: State };
 
@@ -227,7 +229,7 @@ export function noPersist<T extends Persistent<S>, S extends State>(persistent:
                   if (key === PersistentState) {
                       return false;
                   }
-                  if (key == SkipPersistence) {
+                  if (key === SkipPersistence) {
                       return true;
                   }
                   return Reflect.has(target, key);
@@ -279,7 +281,7 @@ globalBus.on("addLayer", (layer: GenericLayer, saveData: Record<string, unknown>
                     // Handle SaveDataPath
                     const newPath = [layer.id, ...path, key];
                     if (
-                        value[SaveDataPath] != undefined &&
+                        value[SaveDataPath] != null &&
                         JSON.stringify(newPath) !== JSON.stringify(value[SaveDataPath])
                     ) {
                         console.error(
diff --git a/src/game/player.ts b/src/game/player.ts
index 5d1142e..322e4db 100644
--- a/src/game/player.ts
+++ b/src/game/player.ts
@@ -64,7 +64,8 @@ export default window.player = player;
 
 /** Convert a player save data object into a JSON string. Unwraps refs. */
 export function stringifySave(player: Player): string {
-    return JSON.stringify(player, (key, value) => unref(value));
+    // Convert undefineds into nulls for proper parsing
+    return JSON.stringify(player, (key, value) => unref(value) ?? null);
 }
 
 declare global {
diff --git a/src/util/save.ts b/src/util/save.ts
index 4137e5b..1578732 100644
--- a/src/util/save.ts
+++ b/src/util/save.ts
@@ -109,7 +109,7 @@ export async function loadSave(playerObj: Partial<Player>): Promise<void> {
         playerObj.time &&
         playerObj.devSpeed !== 0
     ) {
-        if (playerObj.offlineTime == undefined) playerObj.offlineTime = 0;
+        if (playerObj.offlineTime == null) playerObj.offlineTime = 0;
         playerObj.offlineTime += Math.min(
             playerObj.offlineTime + (Date.now() - playerObj.time) / 1000,
             projInfo.offlineLimit * 3600