update tests

Author: pwelter34

src/FluentRest/UrlBuilder.cs

@@ -587,7 +587,7 @@ private void WritePath(StringBuilder builder)
             if (builder.Length > start)
                 builder.Append('/');
 
-            var v = Uri.EscapeDataString(p);
+            var v = Uri.EscapeDataString(p ?? string.Empty);
 
             builder.Append(v);
         }

test/FluentRest.Tests/UrlBuilderTests.cs

@@ -204,4 +204,26 @@ public void BuildBasePath()
         builder.ToString().Should().Be("http://foo.com/test/bar?test=True");
 
     }
+
+    [Fact]
+    public void BuildBaseRelativePath()
+    {
+        var builder = UrlBuilder
+            .Create("/foo")
+            .AppendPath("/bar")
+            .AppendQuery("test", true);
+
+        builder.Scheme.Should().BeEmpty();
+        builder.Host.Should().BeEmpty();
+        builder.Port.Should().BeNull();
+
+        builder.Path.Should().NotBeEmpty();
+        builder.Path.Should().Contain("foo");
+        builder.Path.Should().Contain("bar");
+
+        builder.Query.AllKeys.Length.Should().BeGreaterThan(0);
+        builder.Query.AllKeys.Should().Contain("test");
+
+        builder.ToString().Should().Be("/foo/bar?test=True");
+    }
 }