diff --git a/src/board-manager.ts b/src/board-manager.ts
index eddb820..a9de9ae 100644
--- a/src/board-manager.ts
+++ b/src/board-manager.ts
@@ -430,12 +430,12 @@ export class BoardManager {
   applyTheme(): void {
     const theme = this.settings.boardTheme;
     const colors =
-      theme === 'custom'
-        ? {
-          light: this.settings.lightSquareColor,
-          dark: this.settings.darkSquareColor
-        }
-        : BOARD_THEMES[theme];
+    theme === 'custom'
+      ? {
+        light: this.settings.lightSquareColor,
+        dark: this.settings.darkSquareColor
+      }
+      : BOARD_THEMES[theme] ?? BOARD_THEMES['brown'];
 
     this.container.style.setProperty('--cv-light', colors.light);
     this.container.style.setProperty('--cv-dark', colors.dark);
diff --git a/src/navigation-controller.ts b/src/navigation-controller.ts
index ac407ce..8a3bb21 100644
--- a/src/navigation-controller.ts
+++ b/src/navigation-controller.ts
@@ -407,8 +407,13 @@ export class NavigationController {
     }
 
     const move = this.moves[this.currentMoveIndex - 1];
-    const hasNag = move?.nag;
-    const hasComment = move?.comment;
+    if (!move) {
+      this.commentEl.addClass('hidden');
+      return;
+    }
+
+    const hasNag = !!move.nag;
+    const hasComment = !!move.comment;
 
     if (!hasNag && !hasComment) {
       this.commentEl.addClass('hidden');
@@ -417,12 +422,12 @@ export class NavigationController {
 
     this.commentEl.removeClass('hidden');
 
-    if (hasNag) {
-      const nagClass = NAG_CLASSES[move.nag!] || '';
+    if (hasNag && move.nag) {
+      const nagClass = NAG_CLASSES[move.nag] || '';
       const nagInfo = Object.values(NAG_SYMBOLS).find(
         (n) => n.symbol === move.nag
       );
-      const label = nagInfo ? nagInfo.label : move.nag!;
+      const label = nagInfo ? nagInfo.label : move.nag;
 
       this.commentEl.createSpan({
         cls: `cv-comment-nag ${nagClass}`,
@@ -430,10 +435,10 @@ export class NavigationController {
       });
     }
 
-    if (hasComment) {
+    if (hasComment && move.comment) {
       this.commentEl.createSpan({
         cls: 'cv-comment-text',
-        text: move.comment!
+        text: move.comment
       });
     }
   }
diff --git a/src/parser.ts b/src/parser.ts
index e95b464..dd16e40 100644
--- a/src/parser.ts
+++ b/src/parser.ts
@@ -371,26 +371,26 @@ export function parseMovesFromPgn(
 
       try {
         const result = chess.move(moveStr, { sloppy: true });
-        if (result) {
-          const moveData: MoveData = {
-            san: result.san,
-            from: result.from,
-            to: result.to,
-            fen: chess.fen(),
-            comment: pendingComment,
-            nag: pendingNag,
-            annotations: pendingAnnotation
-          };
+        if (!result) continue;  // change from if (result) { ... } to guard clause
+  
+        const moveData: MoveData = {
+          san: result.san,
+          from: result.from,
+          to: result.to,
+          fen: chess.fen(),
+          comment: pendingComment,
+          nag: pendingNag,
+          annotations: pendingAnnotation
+        };
 
-          if (inlineNag && NAG_SYMBOLS[inlineNag]) {
-            moveData.nag = NAG_SYMBOLS[inlineNag].symbol;
-          }
-
-          moves.push(moveData);
-          pendingComment = undefined;
-          pendingAnnotation = undefined;
-          pendingNag = undefined;
+        if (inlineNag && NAG_SYMBOLS[inlineNag]) {
+          moveData.nag = NAG_SYMBOLS[inlineNag].symbol;
         }
+
+        moves.push(moveData);
+        pendingComment = undefined;
+        pendingAnnotation = undefined;
+        pendingNag = undefined;
       } catch {
         if (warnings) {
           warnings.push(
diff --git a/src/puzzle-controller.ts b/src/puzzle-controller.ts
index 0fc28b2..8dfd9bf 100644
--- a/src/puzzle-controller.ts
+++ b/src/puzzle-controller.ts
@@ -349,8 +349,8 @@ export class PuzzleController {
 
     if (this.data.fen) {
       const parts = this.data.fen.split(/\s+/);
-      if (parts[5]) startMoveNum = parseInt(parts[5]) || 1;
-      if (parts[1] === 'b') startIsBlack = true;
+      startMoveNum = parseInt(parts[5] ?? '1') || 1;
+      startIsBlack = parts[1] === 'b';
     }
 
     let moveNum = startMoveNum;