add zero-length digest test

Author: mgravell

src/StackExchange.Redis/RedisDatabase.cs

@@ -1832,7 +1832,7 @@ public bool LockRelease(RedisKey key, RedisValue value, CommandFlags flags = Com
             if (value.IsNull) throw new ArgumentNullException(nameof(value));
 
             // note that lock tokens are expected to be small, so: we'll use IFEQ rather than IFDEQ, for reliability
-            var features = GetFeatures(key, flags, RedisCommand.SET, out server);
+            var features = GetFeatures(key, flags, RedisCommand.DELEX, out server);
             return features.DeleteWithValueCheck
                 ? GetStringDeleteMessage(key, ValueCondition.Equal(value), flags, caller) // use check-and-delete
                 : null;

tests/StackExchange.Redis.Tests/DigestUnitTests.cs

@@ -57,6 +57,8 @@ public void ValueCondition_ParseDigest(string value)
     [Theory]
     [InlineData("Hello World", "e34615aade2e6333")]
     [InlineData("42", "1217cb28c0ef2191")]
+    [InlineData("", "2d06800538d394c2")]
+    [InlineData("a", "e6c632b61e964e1f")]
     public void KnownXxh3Values(string source, string expected)
         => Assert.Equal(expected, GetXxh3Hex(source));