Fix failing test due to change of behavior: empty body will cause a F…

…lurlParsingException instead of returning null.

test/Flurl.Test/Http/TestingTests.cs

@@ -426,14 +426,12 @@ public class TestingTests : HttpTestFixtureBase
 
 		// https://github.com/tmenier/Flurl/issues/175
 		[Test]
-		public async Task can_deserialize_default_response_more_than_once() {
-			var resp = await "http://www.api.com".GetJsonAsync<object>();
-			Assert.IsNull(resp);
+		public void can_deserialize_default_response_more_than_once()
+		{
+			Assert.ThrowsAsync<FlurlParsingException>(() => "http://www.api.com".GetJsonAsync<object>());
 			// bug: couldn't deserialize here due to reading stream twice
-			resp = await "http://www.api.com".GetJsonAsync<object>();
-			Assert.IsNull(resp);
-			resp = await "http://www.api.com".GetJsonAsync<object>();
-			Assert.IsNull(resp);
+			Assert.ThrowsAsync<FlurlParsingException>(() => "http://www.api.com".GetJsonAsync<object>());
+			Assert.ThrowsAsync<FlurlParsingException>(() => "http://www.api.com".GetJsonAsync<object>());
 		}
 
 		[Test]