diff --git a/src/client/graphics/layers/UnitLayer.ts b/src/client/graphics/layers/UnitLayer.ts
index 4ad9ebea4..51e05a387 100644
--- a/src/client/graphics/layers/UnitLayer.ts
+++ b/src/client/graphics/layers/UnitLayer.ts
@@ -193,7 +193,9 @@ export class UnitLayer implements Layer {
     if (context === null) throw new Error("2d context not supported");
     this.context = context;
     this.transportShipTrailCanvas = document.createElement("canvas");
-    this.unitTrailContext = this.transportShipTrailCanvas.getContext("2d");
+    const trailContext = this.transportShipTrailCanvas.getContext("2d");
+    if (trailContext === null) throw new Error("2d context not supported");
+    this.unitTrailContext = trailContext;
 
     this.canvas.width = this.game.width();
     this.canvas.height = this.game.height();
@@ -219,15 +221,13 @@ export class UnitLayer implements Layer {
   private updateUnitsSprites() {
     const unitsToUpdate = this.game
       .updatesSinceLastTick()
-      ?.[GameUpdateType.Unit]?.map((unit) => this.game.unit(unit.id));
-    unitsToUpdate
-      ?.filter((UnitView) => isSpriteReady(UnitView.type()))
-      .forEach((unitView) => {
-        this.clearUnitCells(unitView);
+      ?.[GameUpdateType.Unit]?.map((unit) => this.game.unit(unit.id))
+      ?.forEach((unitView) => {
+        if (unitView === undefined) return;
+        const ready = isSpriteReady(unitView.type());
+        if (ready) this.clearUnitCells(unitView);
+        this.onUnitEvent(unitView);
       });
-    unitsToUpdate?.forEach((unitView) => {
-      this.onUnitEvent(unitView);
-    });
   }
 
   private clearUnitCells(unit: UnitView) {
@@ -350,7 +350,7 @@ export class UnitLayer implements Layer {
   }
 
   private clearTrail(unit: UnitView) {
-    const trail = this.unitToTrail.get(unit);
+    const trail = this.unitToTrail.get(unit) ?? [];
     const rel = this.relationship(unit);
     for (const t of trail) {
       this.clearCell(this.game.x(t), this.game.y(t), this.unitTrailContext);
@@ -383,7 +383,7 @@ export class UnitLayer implements Layer {
     }
 
     let newTrailSize = 1;
-    const trail = this.unitToTrail.get(unit);
+    const trail = this.unitToTrail.get(unit) ?? [];
     // It can move faster than 1 pixel, draw a line for the trail or else it will be dotted
     if (trail.length >= 1) {
       const cur = {
@@ -443,7 +443,7 @@ export class UnitLayer implements Layer {
     if (!this.unitToTrail.has(unit)) {
       this.unitToTrail.set(unit, []);
     }
-    const trail = this.unitToTrail.get(unit);
+    const trail = this.unitToTrail.get(unit) ?? [];
     trail.push(unit.lastTile());
 
     // Paint trail
@@ -498,15 +498,16 @@ export class UnitLayer implements Layer {
     const x = this.game.x(unit.tile());
     const y = this.game.y(unit.tile());
 
-    let alternateViewColor = null;
+    let alternateViewColor: Colord | null = null;
 
     if (this.alternateView) {
       let rel = this.relationship(unit);
-      if (unit.type() == UnitType.TradeShip && unit.dstPortId() != null) {
-        const target = this.game.unit(unit.dstPortId())?.owner();
+      const dstPortId = unit.dstPortId();
+      if (unit.type() === UnitType.TradeShip && dstPortId !== undefined) {
+        const target = this.game.unit(dstPortId)?.owner();
         const myPlayer = this.game.myPlayer();
-        if (myPlayer != null && target != null) {
-          if (myPlayer == target) {
+        if (myPlayer !== null && target !== undefined) {
+          if (myPlayer === target) {
             rel = Relationship.Self;
           } else if (myPlayer.isFriendly(target)) {
             rel = Relationship.Ally;
@@ -530,7 +531,7 @@ export class UnitLayer implements Layer {
       unit,
       this.theme,
       alternateViewColor ?? customTerritoryColor,
-      alternateViewColor,
+      alternateViewColor ?? undefined,
     );
 
     if (unit.isActive()) {