Fixes #229, bringing HasValue in parity with IsNullOrEmpty (#840)

It appears we just never use this property anywhere and never noticed, but users did long ago. See #229 for details.

Also adds some testing around this. While this may be considered a breaking change, I'm really going to err on the side of this is a plain on bug fix on a rarely used property. This doesn't impact any existing tests.

StackExchange.Redis.Tests/Values.cs

+using System.Linq;
+using System.Text;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace StackExchange.Redis.Tests
+{
+    public class Values : TestBase
+    {
+        public Values(ITestOutputHelper output) : base (output) { }
+
+        [Fact]
+        public void NullValueChecks()
+        {
+            RedisValue four = 4;
+            Assert.False(four.IsNull);
+            Assert.True(four.IsInteger);
+            Assert.True(four.HasValue);
+            Assert.False(four.IsNullOrEmpty);
+
+            RedisValue n = default(RedisValue);
+            Assert.True(n.IsNull);
+            Assert.False(n.IsInteger);
+            Assert.False(n.HasValue);
+            Assert.True(n.IsNullOrEmpty);
+
+            RedisValue emptyArr = new byte[0];
+            Assert.False(emptyArr.IsNull);
+            Assert.False(emptyArr.IsInteger);
+            Assert.False(emptyArr.HasValue);
+            Assert.True(emptyArr.IsNullOrEmpty);
+        }
+    }
+}

StackExchange.Redis/StackExchange/Redis/RedisValue.cs

@@ -47,9 +47,9 @@ private RedisValue(long valueInt64, byte[] valueBlob)
         public bool IsNullOrEmpty => valueBlob == null || (valueBlob.Length == 0 && !(valueBlob == IntegerSentinel));
 
         /// <summary>
-        /// Indicates whether the value is greater than zero-length
+        /// Indicates whether the value is greater than zero-length or has an integer value
         /// </summary>
-        public bool HasValue => valueBlob?.Length > 0;
+        public bool HasValue => !IsNullOrEmpty;
 
         /// <summary>
         /// Indicates whether two RedisValue values are equivalent