From bdf92a9aeac440164a8e07d9a7665df2871059a6 Mon Sep 17 00:00:00 2001
From: Adrian Banks <github@adrianbanks.co.uk>
Date: Wed, 21 Jun 2017 22:53:20 +0100
Subject: [PATCH] Throw a better error when missing conference

Currently, it throws a NullReferenceException and you have to deduce
what is wrong.
---
 DDDEastAnglia/DataAccess/ConferenceLoader.cs      | 15 +++++++++++++--
 .../SimpleData/Builders/ConferenceBuilder.cs      |  5 -----
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/DDDEastAnglia/DataAccess/ConferenceLoader.cs b/DDDEastAnglia/DataAccess/ConferenceLoader.cs
index e595045a..76435ce8 100644
--- a/DDDEastAnglia/DataAccess/ConferenceLoader.cs
+++ b/DDDEastAnglia/DataAccess/ConferenceLoader.cs
@@ -1,6 +1,7 @@
 using System;
 using DDDEastAnglia.DataAccess.SimpleData.Builders;
 using DDDEastAnglia.Domain;
+using Conference = DDDEastAnglia.DataAccess.SimpleData.Models.Conference;
 
 namespace DDDEastAnglia.DataAccess
 {
@@ -36,13 +37,23 @@ public ConferenceLoader(IConferenceRepository conferenceRepository, ConferenceBu
         public IConference LoadConference()
         {
             var dataConference = conferenceRepository.GetByEventShortName(DefaultEventName);
-            return conferenceBuilder.Build(dataConference);
+            return BuildConference(dataConference);
         }
 
         public IConference LoadConference(int sessionId)
         {
             var dataConference = conferenceRepository.ForSession(sessionId);
-            return conferenceBuilder.Build(dataConference);
+            return BuildConference(dataConference);
+        }
+
+        private IConference BuildConference(Conference conference)
+        {
+            if (conference == null)
+            {
+                throw new ArgumentNullException(nameof(conference), "Cannot find current conference");
+            }
+
+            return conferenceBuilder.Build(conference);
         }
     }
 }
diff --git a/DDDEastAnglia/DataAccess/SimpleData/Builders/ConferenceBuilder.cs b/DDDEastAnglia/DataAccess/SimpleData/Builders/ConferenceBuilder.cs
index 4e821c49..f6d1ce75 100644
--- a/DDDEastAnglia/DataAccess/SimpleData/Builders/ConferenceBuilder.cs
+++ b/DDDEastAnglia/DataAccess/SimpleData/Builders/ConferenceBuilder.cs
@@ -17,11 +17,6 @@ public ConferenceBuilder(ICalendarItemRepository calendarItemRepository, IBuild<
 
         public Domain.Conference Build(Conference item)
         {
-            if (item == null)
-            {
-                return null;
-            }
-            
             var conference = new Domain.Conference(item.ConferenceId, item.Name, item.ShortName, item.NumberOfTimeSlots, item.NumberOfTracks, item.AnonymousSessions);
             var calendarItems = calendarItemRepository.GetAll();