Fixed: Error getting candidates if parsed author is null

src/NzbDrone.Core/MediaFiles/BookImport/Identification/CandidateService.cs

@@ -173,10 +173,13 @@ namespace NzbDrone.Core.MediaFiles.BookImport.Identification
             {
                 foreach (var authorTag in authorTags)
                 {
-                    var possibleAuthors = _authorService.GetCandidates(authorTag);
-                    foreach (var author in possibleAuthors)
+                    if (authorTag.IsNotNullOrWhiteSpace())
                     {
-                        candidateReleases.AddRange(GetDbCandidatesByAuthor(localEdition, author, includeExisting));
+                        var possibleAuthors = _authorService.GetCandidates(authorTag);
+                        foreach (var author in possibleAuthors)
+                        {
+                            candidateReleases.AddRange(GetDbCandidatesByAuthor(localEdition, author, includeExisting));
+                        }
                     }
                 }
             }

src/NzbDrone.Core/MediaFiles/BookImport/Identification/IdentificationService.cs

@@ -81,6 +81,7 @@ namespace NzbDrone.Core.MediaFiles.BookImport.Identification
             {
                 i++;
                 _logger.ProgressInfo($"Identifying book {i}/{releases.Count}");
+                _logger.Debug($"Identifying book files:\n{localRelease.LocalBooks.Select(x => x.Path).ConcatToString("\n")}");
                 IdentifyRelease(localRelease, idOverrides, config);
             }