Fix training plan generation flow

server/db.ts

@@ -146,9 +146,9 @@ export async function getUserTrainingPlans(userId: number) {
 
 export async function getActivePlan(userId: number) {
   const db = await getDb();
-  if (!db) return undefined;
+  if (!db) return null;
   const result = await db.select().from(trainingPlans).where(and(eq(trainingPlans.userId, userId), eq(trainingPlans.isActive, 1))).limit(1);
-  return result.length > 0 ? result[0] : undefined;
+  return result.length > 0 ? result[0] : null;
 }
 
 export async function updateTrainingPlan(planId: number, data: Partial<InsertTrainingPlan>) {