Fix saving without changing book edition

src/Readarr.Api.V1/Books/BookController.cs

@@ -167,7 +167,7 @@ namespace Readarr.Api.V1.Books
             var model = bookResource.ToModel(book);
 
             _bookService.UpdateBook(model);
-            _editionService.UpdateMany(model.Editions.Value);
+            _editionService.UpdateMany(model.Editions.Value ?? new List<Edition>());
 
             BroadcastResourceChange(ModelAction.Updated, model.Id);
 

src/Readarr.Api.V1/Books/BookResource.cs

@@ -49,7 +49,7 @@ namespace Readarr.Api.V1.Books
                 return null;
             }
 
-            var selectedEdition = model.Editions?.Value.Where(x => x.Monitored).SingleOrDefault();
+            var selectedEdition = model.Editions?.Value?.SingleOrDefault(x => x.Monitored);
 
             var title = selectedEdition?.Title ?? model.Title;
             var authorTitle = $"{model.Author?.Value?.Metadata?.Value?.SortNameLastFirst} {title}";
@@ -120,7 +120,7 @@ namespace Readarr.Api.V1.Books
 
         public static List<Book> ToModel(this IEnumerable<BookResource> resources)
         {
-            return resources.Select(ToModel).ToList();
+            return resources?.Select(ToModel).ToList();
         }
     }
 }

src/Readarr.Api.V1/Books/EditionResource.cs

@@ -109,7 +109,7 @@ namespace Readarr.Api.V1.Books
 
         public static List<Edition> ToModel(this IEnumerable<EditionResource> resources)
         {
-            return resources.Select(ToModel).ToList();
+            return resources?.Select(ToModel).ToList();
         }
     }
 }