Better null vs empty key prefix handling

StackExchange.Redis.Tests/WithKeyPrefixTests.cs

@@ -8,6 +8,54 @@ namespace StackExchange.Redis.Tests
     [TestFixture]
     public class WithKeyPrefixTests : TestBase
     {
+        [Test]
+        public void BlankPrefixYieldsSame_Bytes()
+        {
+            using (var conn = Create())
+            {
+                var raw = conn.GetDatabase(1);
+                var prefixed = raw.WithKeyPrefix(new byte[0]);
+                Assert.AreSame(raw, prefixed);
+            }
+        }
+        [Test]
+        public void BlankPrefixYieldsSame_String()
+        {
+            using (var conn = Create())
+            {
+                var raw = conn.GetDatabase(1);
+                var prefixed = raw.WithKeyPrefix("");
+                Assert.AreSame(raw, prefixed);
+            }
+        }
+        [Test, ExpectedException(typeof(ArgumentNullException))]
+        public void NullPrefixIsError_Bytes()
+        {
+            using (var conn = Create())
+            {
+                var raw = conn.GetDatabase(1);
+                var prefixed = raw.WithKeyPrefix((string)null);
+            }
+        }
+        [Test, ExpectedException(typeof(ArgumentNullException))]
+        public void NullPrefixIsError_String()
+        {
+            using (var conn = Create())
+            {
+                var raw = conn.GetDatabase(1);
+                var prefixed = raw.WithKeyPrefix((string)null);
+            }
+        }
+
+        [Test, ExpectedException(typeof(ArgumentNullException))]
+        [TestCase("abc")]
+        [TestCase("")]
+        [TestCase(null)]
+        public void NullDatabaseIsError(string prefix)
+        {
+            IDatabase raw = null;
+            var prefixed = raw.WithKeyPrefix(prefix);
+        }
         [Test]
         public void BasicSmokeTest()
         {
@@ -15,13 +63,6 @@ public void BasicSmokeTest()
             {
                 var raw = conn.GetDatabase(1);
 
-                var vanilla = raw.WithKeyPrefix("");
-                Assert.AreSame(raw, vanilla);
-                vanilla = raw.WithKeyPrefix((byte[])null);
-                Assert.AreSame(raw, vanilla);
-                vanilla = raw.WithKeyPrefix((string)null);
-                Assert.AreSame(raw, vanilla);
-
                 var foo = raw.WithKeyPrefix("foo");
                 var foobar = foo.WithKeyPrefix("bar");
 

StackExchange.Redis/StackExchange/Redis/KeyspaceIsolation/DatabaseExtension.cs

@@ -44,7 +44,12 @@ public static IDatabase WithKeyPrefix(this IDatabase database, RedisKey keyPrefi
                 throw new ArgumentNullException("database");
             }
 
-            if (keyPrefix.IsNull || keyPrefix.Value.Length == 0)
+            if (keyPrefix.IsNull)
+            {
+                throw new ArgumentNullException("keyPrefix");
+            }
+
+            if (keyPrefix.Value.Length == 0)
             {
                 return database; // fine - you can keep using the original, then
             }