Fix not supported exceptions

Author: JimBobSquarePants

src/ImageSharp.Web/Commands/Converters/EnumConverter.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors.
+// Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
 using System;
@@ -15,10 +15,9 @@ internal sealed class EnumConverter : CommandConverter
         /// <inheritdoc/>
         public override object ConvertFrom(CultureInfo culture, string value, Type propertyType)
         {
-            if (value == null)
+            if (string.IsNullOrWhiteSpace(value))
             {
-                // TODO: How can we get the default enum, or should we return null?
-                return base.ConvertFrom(culture, null, propertyType);
+                return Activator.CreateInstance(propertyType);
             }
 
             try
@@ -51,4 +50,4 @@ public override object ConvertFrom(CultureInfo culture, string value, Type prope
         /// <returns>The <see cref="T:String[]"/>.</returns>
         private static string[] GetStringArray(string input, char separator) => input.Split(separator).Select(s => s.Trim()).ToArray();
     }
-}
+}

src/ImageSharp.Web/Commands/Converters/IntegralNumberConverter.cs

@@ -16,9 +16,10 @@ internal sealed class IntegralNumberConverter<T> : CommandConverter
         /// <inheritdoc/>
         public override object ConvertFrom(CultureInfo culture, string value, Type propertyType)
         {
-            if (value == null || Array.IndexOf(TypeConstants.IntegralTypes, propertyType) < 0)
+            if (string.IsNullOrWhiteSpace(value)
+                || Array.IndexOf(TypeConstants.IntegralTypes, propertyType) < 0)
             {
-                return base.ConvertFrom(culture, null, propertyType);
+                return default(T);
             }
 
             // Round the value to the nearest decimal value

src/ImageSharp.Web/Commands/Converters/ListConverter{T}.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors.
+// Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
 using System;
@@ -17,6 +17,12 @@ internal class ListConverter<T> : CommandConverter
         /// <inheritdoc/>
         public override object ConvertFrom(CultureInfo culture, string value, Type propertyType)
         {
+            var result = new List<T>();
+            if (string.IsNullOrWhiteSpace(value))
+            {
+                return result;
+            }
+
             Type type = typeof(T);
             ICommandConverter paramConverter = CommandDescriptor.GetConverter(type);
 
@@ -25,17 +31,12 @@ public override object ConvertFrom(CultureInfo culture, string value, Type prope
                 throw new InvalidOperationException("No type converter exists for type " + type.FullName);
             }
 
-            var result = new List<T>();
-
-            if (value != null)
+            foreach (string pill in this.GetStringArray(value, culture))
             {
-                foreach (string pill in this.GetStringArray(value, culture))
+                object item = paramConverter.ConvertFromInvariantString(pill, type);
+                if (item != null)
                 {
-                    object item = paramConverter.ConvertFromInvariantString(pill, type);
-                    if (item != null)
-                    {
-                        result.Add((T)item);
-                    }
+                    result.Add((T)item);
                 }
             }
 
@@ -54,4 +55,4 @@ protected string[] GetStringArray(string input, CultureInfo culture)
             return input.Split(separator).Select(s => s.Trim()).ToArray();
         }
     }
-}
+}

src/ImageSharp.Web/Commands/Converters/SimpleCommandConverter{T}.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors.
+// Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
 using System;
@@ -16,7 +16,7 @@ internal sealed class SimpleCommandConverter<T> : CommandConverter
         /// <inheritdoc/>
         public override object ConvertFrom(CultureInfo culture, string value, Type propertyType)
         {
-            if (value == null)
+            if (string.IsNullOrWhiteSpace(value))
             {
                 return default(T);
             }
@@ -32,4 +32,4 @@ public override object ConvertFrom(CultureInfo culture, string value, Type prope
             return (T)Convert.ChangeType(value, t, culture);
         }
     }
-}
+}