diff --git a/src/field/pokemon.ts b/src/field/pokemon.ts
index 7117068d5de..71e0ae68179 100644
--- a/src/field/pokemon.ts
+++ b/src/field/pokemon.ts
@@ -197,7 +197,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
       this.fusionVariant = dataSource.fusionVariant || 0;
       this.fusionGender = dataSource.fusionGender;
       this.fusionLuck = dataSource.fusionLuck;
-      this.usedTMs = dataSource.usedTMs || [];
+      this.usedTMs = dataSource.usedTMs ?? [];
     } else {
       this.id = Utils.randSeedInt(4294967296);
       this.ivs = ivs || Utils.getIvsFromId(this.id);
@@ -936,7 +936,9 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
     if (this.metBiome === -1 && !this.scene.gameMode.isFreshStartChallenge() && !this.scene.gameMode.isDaily) {
       levelMoves = this.getUnlockedEggMoves().concat(levelMoves);
     }
-    levelMoves = this.usedTMs?.length? this.usedTMs.filter(m => !levelMoves.includes(m)).concat(levelMoves) : levelMoves;
+    if (Array.isArray(this.usedTMs) && this.usedTMs.length > 0) {
+      levelMoves = this.usedTMs.filter(m => !levelMoves.includes(m)).concat(levelMoves);
+    }
     levelMoves = levelMoves.filter(lm => !this.moveset.some(m => m?.moveId === lm));
     return levelMoves;
   }
diff --git a/src/phases/learn-move-phase.ts b/src/phases/learn-move-phase.ts
index e128d390463..c3fb2a6d5ea 100644
--- a/src/phases/learn-move-phase.ts
+++ b/src/phases/learn-move-phase.ts
@@ -18,7 +18,7 @@ export class LearnMovePhase extends PlayerPartyMemberPokemonPhase {
     super(scene, partyMemberIndex);
 
     this.moveId = moveId;
-    this.fromTM = fromTM || false;
+    this.fromTM = fromTM ?? false;
   }
 
   start() {
diff --git a/src/system/pokemon-data.ts b/src/system/pokemon-data.ts
index 4adca443e60..928077608ed 100644
--- a/src/system/pokemon-data.ts
+++ b/src/system/pokemon-data.ts
@@ -99,7 +99,7 @@ export default class PokemonData {
     this.fusionVariant = source.fusionVariant;
     this.fusionGender = source.fusionGender;
     this.fusionLuck = source.fusionLuck !== undefined ? source.fusionLuck : (source.fusionShiny ? source.fusionVariant + 1 : 0);
-    this.usedTMs = source.usedTMs || [];
+    this.usedTMs = source.usedTMs ?? [];
 
     if (!forHistory) {
       this.boss = (source instanceof EnemyPokemon && !!source.bossSegments) || (!this.player && !!source.boss);