add error handling

Emby.Server.Implementations/Library/LibraryManager.cs

@@ -2593,7 +2593,7 @@ namespace Emby.Server.Implementations.Library
                 {
                     foreach (var pathInfo in libraryOptions.PathInfos)
                     {
-                        if (string.IsNullOrWhiteSpace(pathInfo.NetworkPath))
+                        if (string.IsNullOrWhiteSpace(pathInfo.Path) || string.IsNullOrWhiteSpace(pathInfo.NetworkPath))
                         {
                             continue;
                         }
@@ -2620,6 +2620,8 @@ namespace Emby.Server.Implementations.Library
             }
 
             foreach (var map in ConfigurationManager.Configuration.PathSubstitutions)
+            {
+                if (!string.IsNullOrWhiteSpace(map.From))
                 {
                     var substitutionResult = SubstitutePathInternal(path, map.From, map.To);
                     if (substitutionResult.Item2)
@@ -2627,6 +2629,7 @@ namespace Emby.Server.Implementations.Library
                         return substitutionResult.Item1;
                     }
                 }
+            }
 
             return path;
         }