refactored error handling

api/Services/PersonService.cs

@@ -33,7 +33,7 @@ namespace api.Services
 
         public async Task<PersonDto> GetPersonByUsernameAsync(string username)
         {
-            Person person = await personExists(username);
+            Person person = await PersonExists(username);
 
             return new PersonDto
             {
@@ -46,7 +46,7 @@ namespace api.Services
         public async Task UpdatePersonAsync(string username, PersonDto personDto)
         {
 
-            await personExists(username);
+            await PersonExists(username);
 
             Person updatedPerson = Person.Create(username: username, realName: personDto.RealName, birthday: personDto.Birthday);
             await _personRepository.UpdateAsync(updatedPerson);
@@ -54,18 +54,16 @@ namespace api.Services
 
         public async Task DeletePersonAsync(string username)
         {
-            await personExists(username);
+            await PersonExists(username);
 
             await _personRepository.DeleteAsync(username);
         }
 
-        private async Task<Person> personExists(string username)
+        private async Task<Person> PersonExists(string username)
         {
             username = Person.NormalizeUsername(username);
 
-            Person? person = await _personRepository.GetByUsernameAsync(username);
-            
-            if (person == null) throw new KeyNotFoundException($"Person '{username}' not found");
+            Person person = await _personRepository.GetByUsernameAsync(username);
 
             return person;
         }