Minor code fixes

src/Stripe.net/Infrastructure/JsonConverters/ExpandableFieldConverter.cs

@@ -44,7 +44,7 @@ public override void WriteJson(JsonWriter writer, object value, JsonSerializer s
                 default:
                     throw new JsonSerializationException(string.Format(
                         "Unexpected value when converting ExpandableField. Expected IExpandableField, got {0}.",
-                        value.GetType().ToString()));
+                        value.GetType()));
             }
         }
 

src/Stripe.net/Infrastructure/StringUtils.cs

@@ -2,7 +2,7 @@ namespace Stripe.Infrastructure
 {
     using System.Text.RegularExpressions;
 
-    internal class StringUtils
+    internal static class StringUtils
     {
         /// <summary>Converts the string to snake case.</summary>
         /// <param name="str">The string to convert.</param>

src/StripeTests/Services/AccountLinks/AccountLinkServiceTest.cs

@@ -9,15 +9,15 @@ namespace StripeTests
 
     public class AccountLinkServiceTest : BaseStripeTest
     {
-        private AccountLinkService service;
-        private AccountLinkCreateOptions createOptions;
+        private readonly AccountLinkService service;
+        private readonly AccountLinkCreateOptions createOptions;
 
         public AccountLinkServiceTest(MockHttpClientFixture mockHttpClientFixture)
             : base(mockHttpClientFixture)
         {
             this.service = new AccountLinkService();
 
-            this.createOptions = new AccountLinkCreateOptions()
+            this.createOptions = new AccountLinkCreateOptions
             {
                 AccountId = "acct_123",
                 Collect = "eventually_due",

src/StripeTests/Services/AutoPagingTest.cs

@@ -45,7 +45,7 @@ public void ListAutoPaging()
 
             // Call auto-paging method
             var service = new PageableService();
-            var options = new ListOptions()
+            var options = new ListOptions
             {
                 Limit = 2,
             };

src/StripeTests/Services/Events/EventUtilityTest.cs

@@ -77,9 +77,9 @@ public void AcceptsExpectedApiVersion()
         {
             var evt = Event.FromJson(this.json);
             evt.ApiVersion = StripeConfiguration.ApiVersion;
-            var json = evt.ToJson();
+            var serialized = evt.ToJson();
 
-            evt = EventUtility.ParseEvent(json);
+            evt = EventUtility.ParseEvent(serialized);
             Assert.Equal(StripeConfiguration.ApiVersion, evt.ApiVersion);
         }