Fix remaining technical debt bugs

- Bug-001: Add null check for SingleOrDefault() in TorrentRssParser
- Bug-006: Replace generic Exception with PathCombinationException in OsPath
- Bug-006: Replace generic Exception with NotSupportedException in IMDbListRequestGenerator

src/NzbDrone.Common/Disk/OsPath.cs

@@ -421,7 +421,7 @@ public bool Equals(OsPath other, bool ignoreTrailingSlash)
         {
             if (left.Kind != right.Kind && right.Kind != OsPathKind.Unknown)
             {
-                throw new Exception(string.Format("Cannot combine OsPaths of different platforms ('{0}' + '{1}')", left, right));
+                throw new PathCombinationException("Cannot combine OsPaths of different platforms ('{0}' + '{1}')", left, right);
             }
 
             if (right.IsEmpty)

src/NzbDrone.Common/Disk/PathCombinationException.cs

@@ -0,0 +1,17 @@
+using NzbDrone.Common.Exceptions;
+
+namespace NzbDrone.Common.Disk
+{
+    public class PathCombinationException : NzbDroneException
+    {
+        public PathCombinationException(string message, params object[] args)
+            : base(message, args)
+        {
+        }
+
+        public PathCombinationException(string message)
+            : base(message)
+        {
+        }
+    }
+}

src/NzbDrone.Core/ImportLists/RadarrList2/IMDb/IMDbListRequestGenerator.cs

@@ -14,7 +14,7 @@ protected override HttpRequest GetHttpRequest()
             // Use IMDb list Export for user lists to bypass RadarrAPI caching
             if (Settings.ListId.StartsWith("ls", StringComparison.OrdinalIgnoreCase))
             {
-                throw new Exception("IMDb lists of the form 'ls12345678' are no longer supported. Feel free to remove this list after you review your Clean Library Level.");
+                throw new NotSupportedException("IMDb lists of the form 'ls12345678' are no longer supported. Feel free to remove this list after you review your Clean Library Level.");
             }
 
             var request = RequestBuilder.Create()

src/NzbDrone.Core/Indexers/TorrentRssParser.cs

@@ -168,7 +168,10 @@ protected virtual string GetMagnetUrl(XElement item)
             if (PeersElementName.IsNotNullOrWhiteSpace())
             {
                 var itempeers = item.FindDecendants(PeersElementName).SingleOrDefault();
-                return int.Parse(itempeers.Value);
+                if (itempeers != null)
+                {
+                    return int.Parse(itempeers.Value);
+                }
             }
 
             return null;