Added unit test to cover zero probability vowels:

- When empty string generation is turned on, a SyllableGenerator should not throw any exceptions if its graphemes have been set to a zero probability of appearing
- In this scenario, a NameGenerator using a zero-probability SyllableGenerator should only be generating empty strings

Syllabore/Syllabore.Tests/SyllableGeneratorTests.cs

@@ -219,7 +219,23 @@ public void NameGenerator_OnlyVowelsWithNoConsonants_GenerationSuccessful()
             {
                 // Check that the name generator generates nothing but the vowels
                 var name = ng.Next();
-                Assert.IsTrue(!string.IsNullOrEmpty(name) && Regex.IsMatch(name, "^[aeiouAEIOU]+$"));
+                Assert.IsTrue(Regex.IsMatch(name, "^[aeiouAEIOU]+$"));
+            }
+        }
+
+        [TestMethod]
+        public void NameGenerator_ZeroProbabilityVowelsButEmptyStringsEnabled_GenerationSuccessful()
+        {
+            var sut = new SyllableGenerator()
+                .WithVowels("aeiou")
+                .WithProbability(x => x.OfVowels(0.0))
+                .AllowEmptyStrings(true);
+
+            var ng = new NameGenerator(sut);
+
+            for (int i = 0; i < 1000; i++)
+            {
+                Assert.IsTrue(ng.Next() == string.Empty);
             }
         }