From 27773caa2830ea569ae9fdf1385cd450fb35dcce Mon Sep 17 00:00:00 2001
From: Jonas Dellinger <jonas@dellinger.dev>
Date: Mon, 29 Jun 2020 22:42:35 +0200
Subject: [PATCH] Empty lists are correctly excluded from query params, fixes
 #471

---
 SpotifyAPI.Web.Tests/Models/RequestParamsTest.cs | 15 +++++++++++++++
 SpotifyAPI.Web/Models/Request/RequestParams.cs   |  9 ++++++---
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/SpotifyAPI.Web.Tests/Models/RequestParamsTest.cs b/SpotifyAPI.Web.Tests/Models/RequestParamsTest.cs
index bad04d30..767ab937 100644
--- a/SpotifyAPI.Web.Tests/Models/RequestParamsTest.cs
+++ b/SpotifyAPI.Web.Tests/Models/RequestParamsTest.cs
@@ -36,6 +36,15 @@ namespace SpotifyAPI.Web.Tests
       Assert.AreEqual("{\"first\":true}", firstParams.ToString(Formatting.None));
       Assert.AreEqual("{\"second\":false}", secondParams.ToString(Formatting.None));
     }
+
+    [Test]
+    public void EmptyListIsSkippedInQueryParams()
+    {
+      var first = new EmptyListExampleRequestModel();
+      Assert.AreEqual(new Dictionary<string, string> { }, first.BuildQueryParams());
+      first.List.Add("hello_world");
+      Assert.AreEqual(new Dictionary<string, string> { { "list", "hello_world" } }, first.BuildQueryParams());
+    }
   }
 
   public class FirstRequestModel : RequestParams
@@ -51,4 +60,10 @@ namespace SpotifyAPI.Web.Tests
     [QueryParam("second")]
     public bool? Second { get; set; }
   }
+
+  public class EmptyListExampleRequestModel : RequestParams
+  {
+    [QueryParam("list")]
+    public IList<string> List { get; set; } = new List<string>();
+  }
 }
diff --git a/SpotifyAPI.Web/Models/Request/RequestParams.cs b/SpotifyAPI.Web/Models/Request/RequestParams.cs
index da3c52d1..4cf451d9 100644
--- a/SpotifyAPI.Web/Models/Request/RequestParams.cs
+++ b/SpotifyAPI.Web/Models/Request/RequestParams.cs
@@ -97,10 +97,13 @@ namespace SpotifyAPI.Web
       object value = prop.GetValue(this);
       if (value != null)
       {
-        if (value is IList<string> list && list.Count > 0)
+        if (value is IList<string> list)
         {
-          var str = string.Join(",", list);
-          queryParams.Add(attribute.Key ?? prop.Name, str);
+          if (list.Count > 0)
+          {
+            var str = string.Join(",", list);
+            queryParams.Add(attribute.Key ?? prop.Name, str);
+          }
         }
         else if (value is bool valueAsBool)
         {