Fixed: Error getting candidates if parsed author is null

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

@@ -172,6 +172,8 @@ namespace NzbDrone.Core.MediaFiles.BookImport.Identification
             if (authorTags.Any())
             {
                 foreach (var authorTag in authorTags)
+                {
+                    if (authorTag.IsNotNullOrWhiteSpace())
                     {
                         var possibleAuthors = _authorService.GetCandidates(authorTag);
                         foreach (var author in possibleAuthors)
@@ -180,6 +182,7 @@ namespace NzbDrone.Core.MediaFiles.BookImport.Identification
                         }
                     }
                 }
+            }
 
             return candidateReleases;
         }

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);
             }