Revert use of explicit converters that prevent APIs from returning null.

Author: Tratcher

src/Microsoft.AspNet.Http.Extensions/HeaderDictionaryExtensions.cs

@@ -36,7 +36,7 @@ public static void AppendCommaSeparatedValues(this IHeaderDictionary headers, st
         /// <returns>the associated values from the collection separated into individual values, or StringValues.Empty if the key is not present.</returns>
         public static string[] GetCommaSeparatedValues(this IHeaderDictionary headers, string key)
         {
-            return ParsingHelpers.GetHeaderSplit(headers, key).ToArray();
+            return ParsingHelpers.GetHeaderSplit(headers, key);
         }
 
         /// <summary>

src/Microsoft.AspNet.Http.Extensions/HeaderDictionaryTypeExtensions.cs

@@ -179,7 +179,7 @@ internal static T Get<T>(this IHeaderDictionary headers, string name)
             if (KnownParsers.TryGetValue(typeof(T), out temp))
             {
                 var func = (Func<string, T>)temp;
-                return func(headers[name].ToString());
+                return func(headers[name]);
             }
 
             var value = headers[name];
@@ -202,7 +202,7 @@ internal static IList<T> GetList<T>(this IHeaderDictionary headers, string name)
             if (KnownListParsers.TryGetValue(typeof(T), out temp))
             {
                 var func = (Func<IList<string>, IList<T>>)temp;
-                return func(headers[name].ToArray());
+                return func(headers[name]);
             }
 
             var values = headers[name];

src/Microsoft.AspNet.Http.Extensions/Internal/ParsingHelpers.cs

@@ -126,7 +126,7 @@ public static void AppendHeaderJoined(IHeaderDictionary headers, string key, par
                 return;
             }
 
-            string existing = GetHeader(headers, key).ToString();
+            string existing = GetHeader(headers, key);
             if (existing == null)
             {
                 SetHeaderJoined(headers, key, values);

src/Microsoft.AspNet.Http.Extensions/RequestHeaders.cs

@@ -170,7 +170,7 @@ public HostString Host
         {
             get
             {
-                return HostString.FromUriComponent(Headers[HeaderNames.Host].ToString());
+                return HostString.FromUriComponent(Headers[HeaderNames.Host]);
             }
             set
             {

src/Microsoft.AspNet.Http.Extensions/ResponseHeaders.cs

@@ -134,7 +134,7 @@ public Uri Location
             get
             {
                 Uri uri;
-                if (Uri.TryCreate(Headers[HeaderNames.Location].ToString(), UriKind.RelativeOrAbsolute, out uri))
+                if (Uri.TryCreate(Headers[HeaderNames.Location], UriKind.RelativeOrAbsolute, out uri))
                 {
                     return uri;
                 }

src/Microsoft.AspNet.Http/DefaultHttpRequest.cs

@@ -140,7 +140,7 @@ public override bool IsHttps
 
         public override HostString Host
         {
-            get { return HostString.FromUriComponent(Headers["Host"].ToString()); }
+            get { return HostString.FromUriComponent(Headers["Host"]); }
             set { Headers["Host"] = value.ToUriComponent(); }
         }
 

src/Microsoft.AspNet.Http/DefaultHttpResponse.cs

@@ -87,7 +87,7 @@ public override string ContentType
         {
             get
             {
-                return Headers[HeaderNames.ContentType].ToString();
+                return Headers[HeaderNames.ContentType];
             }
             set
             {

src/Microsoft.AspNet.Http/DefaultWebSocketManager.cs

@@ -55,7 +55,7 @@ public override IList<string> WebSocketRequestedProtocols
         {
             get
             {
-                return ParsingHelpers.GetHeaderSplit(HttpRequestFeature.Headers, HeaderNames.WebSocketSubProtocols).ToArray();
+                return ParsingHelpers.GetHeaderSplit(HttpRequestFeature.Headers, HeaderNames.WebSocketSubProtocols);
             }
         }
 

src/Microsoft.AspNet.Http/Features/FormFile.cs

@@ -21,13 +21,13 @@ public FormFile(Stream baseStream, long baseStreamOffset, long length)
 
         public string ContentDisposition
         {
-            get { return Headers["Content-Disposition"].ToString(); }
+            get { return Headers["Content-Disposition"]; }
             set { Headers["Content-Disposition"] = value; }
         }
 
         public string ContentType
         {
-            get { return Headers["Content-Type"].ToString(); }
+            get { return Headers["Content-Type"]; }
             set { Headers["Content-Type"] = value; }
         }
 

src/Microsoft.AspNet.Http/RequestCookieCollection.cs

@@ -48,15 +48,15 @@ public string this[string key]
 
                 if (Store == null)
                 {
-                    return string.Empty;
+                    return null;
                 }
 
                 string value;
                 if (TryGetValue(key, out value))
                 {
                     return value;
                 }
-                return string.Empty;
+                return null;
             }
         }
 
@@ -126,7 +126,7 @@ public bool TryGetValue(string key, out string value)
         {
             if (Store == null)
             {
-                value = string.Empty;
+                value = null;
                 return false;
             }
             return Store.TryGetValue(key, out value);

src/Microsoft.AspNet.WebUtilities/MultipartReader.cs

@@ -87,7 +87,7 @@ private async Task<Dictionary<string, StringValues>> ReadHeadersAsync(Cancellati
                     throw new InvalidOperationException("Total header size limit exceeded: " + TotalHeaderSizeLimit.ToString());
                 }
                 int splitIndex = line.IndexOf(':');
-                Debug.Assert(splitIndex > 0, $"Invalid header line: {line.ToString()}");
+                Debug.Assert(splitIndex > 0, $"Invalid header line: {line}");
                 if (splitIndex >= 0)
                 {
                     var name = line.Substring(0, splitIndex);

src/Microsoft.AspNet.WebUtilities/MultipartSection.cs

@@ -16,7 +16,7 @@ public string ContentType
                 StringValues values;
                 if (Headers.TryGetValue("Content-Type", out values))
                 {
-                    return values.ToString();
+                    return values;
                 }
                 return null;
             }
@@ -29,7 +29,7 @@ public string ContentDisposition
                 StringValues values;
                 if (Headers.TryGetValue("Content-Disposition", out values))
                 {
-                    return values.ToString();
+                    return values;
                 }
                 return null;
             }