Fixed: Identification failing if book metadata has no authors

src/NzbDrone.Core.Test/MediaFiles/TrackImport/Identification/DistanceFixture.cs

@@ -131,6 +131,38 @@ namespace NzbDrone.Core.Test.MediaFiles.BookImport.Identification
             dist.Penalties.Should().BeEquivalentTo(new Dictionary<string, List<double>> { { "string", new List<double> { 0.0 } } });
         }
 
+        [Test]
+        public void test_add_string_empty_values_valid_target()
+        {
+            var dist = new Distance();
+            dist.AddString("string", new List<string>(), "target");
+            dist.Penalties.Should().BeEquivalentTo(new Dictionary<string, List<double>> { { "string", new List<double> { 1.0 } } });
+        }
+
+        [Test]
+        public void test_add_string_empty_values_empty_target()
+        {
+            var dist = new Distance();
+            dist.AddString("string", new List<string>(), string.Empty);
+            dist.Penalties.Should().BeEquivalentTo(new Dictionary<string, List<double>> { { "string", new List<double> { 0.0 } } });
+        }
+
+        [Test]
+        public void test_add_string_empty_options_valid_value()
+        {
+            var dist = new Distance();
+            dist.AddString("string", "value", new List<string>());
+            dist.Penalties.Should().BeEquivalentTo(new Dictionary<string, List<double>> { { "string", new List<double> { 1.0 } } });
+        }
+
+        [Test]
+        public void test_add_string_empty_options_empty_value()
+        {
+            var dist = new Distance();
+            dist.AddString("string", string.Empty, new List<string>());
+            dist.Penalties.Should().BeEquivalentTo(new Dictionary<string, List<double>> { { "string", new List<double> { 0.0 } } });
+        }
+
         [Test]
         public void test_distance()
         {

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

@@ -150,14 +150,28 @@ namespace NzbDrone.Core.MediaFiles.BookImport.Identification
         }
 
         public void AddString(string key, string value, List<string> options)
+        {
+            if (!options.Any())
+            {
+                Add(key, StringScore(value, string.Empty));
+            }
+            else
             {
                 Add(key, options.Min(x => StringScore(value, x)));
             }
+        }
 
         public void AddString(string key, List<string> values, string target)
+        {
+            if (!values.Any())
+            {
+                Add(key, StringScore(string.Empty, target));
+            }
+            else
             {
                 Add(key, values.Min(v => StringScore(v, target)));
             }
+        }
 
         public void AddBool(string key, bool expr)
         {