#74: Fix for empty (not null) header values (#75)

* #74: Fix for empty (not null) header values

* 74: Add tests for header value extension

Author: WebDucer

src/GitLabApiClient/Internal/Http/GitLabApiPagedRequestor.cs

@@ -1,8 +1,9 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Net.Http.Headers;
 using System.Threading.Tasks;
+using GitLabApiClient.Internal.Utilities;
 
 namespace GitLabApiClient.Internal.Http
 {
@@ -107,7 +108,7 @@ public static T GetFirstHeaderValueOrDefault<T>(
                 return toReturn;
 
             string valueString = headerValues.FirstOrDefault();
-            return valueString == null ? toReturn : (T)Convert.ChangeType(valueString, typeof(T));
+            return valueString.IsNullOrEmpty() ? toReturn : (T)Convert.ChangeType(valueString, typeof(T));
         }
     }
 }

test/GitLabApiClient.Test/Internal/Http/HttpResponseHeadersExtensionsTest.cs

@@ -0,0 +1,54 @@
+using System.Net;
+using System.Net.Http;
+using System.Net.Http.Headers;
+using FluentAssertions;
+using GitLabApiClient.Internal.Http;
+using Xunit;
+
+namespace GitLabApiClient.Test.Internal.Http
+{
+    public class HttpResponseHeadersExtensionsTest
+    {
+        private HttpResponseHeaders GetTestHeaders()
+        {
+            var response = new HttpResponseMessage(HttpStatusCode.Created);
+            response.Headers.Add("X-Fifty-Five", "55");
+            response.Headers.Add("X-Empty", "");
+
+            return response.Headers;
+        }
+
+        [Fact]
+        public void GetFirstHeaderValueOrDefault_WithEmptyValue_ReturnDefaultValue()
+        {
+            int expected = 0;
+            var sut = GetTestHeaders();
+
+            int result = sut.GetFirstHeaderValueOrDefault<int>("X-Empty");
+
+            result.Should().Be(expected);
+        }
+
+        [Fact]
+        public void GetFirstHeaderValueOrDefault_WithNotExistingKey_ReturnDefaultValue()
+        {
+            int expected = 0;
+            var sut = GetTestHeaders();
+
+            int result = sut.GetFirstHeaderValueOrDefault<int>("X-Not-Exists");
+
+            result.Should().Be(expected);
+        }
+
+        [Fact]
+        public void GetFirstHeaderValueOrDefault_WithValue_ReturnValue()
+        {
+            int expected = 55;
+            var sut = GetTestHeaders();
+
+            int result = sut.GetFirstHeaderValueOrDefault<int>("X-Fifty-Five");
+
+            result.Should().Be(expected);
+        }
+    }
+}