Update stopwatch string

BritishHorseRacingApi.Tests/DataConverterHelperTests.cs

@@ -22,6 +22,19 @@ namespace BritishHorseRacingApi.Tests
             Assert.Equal(milliseconds, timeSpan.Milliseconds);
         }
 
+        [Theory()]
+        [InlineData("", null)]
+        [InlineData(null, null)]
+        [InlineData(" ", null)]
+        public void TestStopWatchStringConversionForEmpty(string time, double? expectedValue)
+        {
+            //Arrange
+            //Act
+            var totalMilliseconds = DataConverterHelper.StopWatchStringToMilliseconds(time);
+            //Assert
+            Assert.Equal(totalMilliseconds, expectedValue);
+        }
+
         [Theory()]
         [InlineData("1m 1f 104y", 2084)]
         [InlineData("1f 104y", 324)]

BritishHorseRacingApi/Helpers/DataConverterHelper.cs

@@ -9,6 +9,8 @@ namespace BritishHorseRacingApi.Helpers
         private static Regex _stopwatchTimeRegex = new Regex(@"^(?'minutes'[0-9]*(?=m))?m? ?(?'seconds'[0-9\.]*)s ?(?:\(\+)?(?'lossDifference'[0-9\.]*)(?:s\))?", RegexOptions.Compiled);
         public static int? StopWatchStringToMilliseconds(string stopwatchValue)
         {
+            if (String.IsNullOrWhiteSpace(stopwatchValue))
+                return null;
             var match = _stopwatchTimeRegex.Match(stopwatchValue);
             var minutes = GetComponent(match, "minutes", 0);
             var secondsAndMilliseconds = GetComponent(match, "seconds", "0").Split('.');