refactored error handling

api/Repositories/PersonRepository.cs

@@ -20,7 +20,7 @@ public class PersonRepository(AppDbContext context) : IPersonRepository
 
     public async Task<Person> GetByUsernameAsync(string username)
     {
-        return await _context.Persons.FindAsync(username);
+        return await _context.Persons.FindAsync(username) ?? throw new KeyNotFoundException("User does not exist");
     }
     public async Task UpdateAsync(Person person)
     {
@@ -30,14 +30,12 @@ public class PersonRepository(AppDbContext context) : IPersonRepository
 
     public async Task DeleteAsync(string username)
     {
-        Person person = await _context.Persons.FindAsync(username);
+        Person person = await _context.Persons.FindAsync(username)  ?? throw new KeyNotFoundException("User does not exist");;
 
-        if (person != null)
-        {
             _context.Persons.Remove(person);
 
             await _context.SaveChangesAsync();
-        }
+        
     }