Allow null Option.DefaultValue

Author: Adam Byrd

src/CommandLine.Tests/CommandLine.Tests.csproj

@@ -59,6 +59,7 @@
       <Link>Properties\SharedAssemblyInfo.cs</Link>
     </Compile>
     <Compile Include="Fakes\FakeOptionsWithNullable.cs" />
+    <Compile Include="Fakes\FakeOptionsWithNullDefault.cs" />
     <Compile Include="Fakes\FakeOptionsWithTwoIntegers.cs" />
     <Compile Include="Fakes\FakeInterfaceOptions.cs" />
     <Compile Include="Fakes\FakeOptionsWithHelpTextEnum.cs" />

src/CommandLine.Tests/Fakes/FakeOptionsWithNullDefault.cs

@@ -0,0 +1,15 @@
+using System.Collections.Generic;
+
+namespace CommandLine.Tests.Fakes
+{
+    class FakeOptionsWithNullDefault
+    {
+        [Option('i', DefaultValue = null)]
+        public IEnumerable<int> IntSequence
+		{
+			get { return intSequence; }
+			set { intSequence = value; }
+		}
+		private IEnumerable<int> intSequence;
+    }
+}

src/CommandLine.Tests/Unit/ParserTests.cs

@@ -247,5 +247,19 @@ public void Parse_nullable_options()
             Assert.False(result.Errors.Any());
             // Teardown
         }
+
+        [Fact]
+        public void Parse_allow_null_default_value()
+        {
+            // Fixture setup
+            var sut = new Parser();
+
+            // Exercize system
+            var result = sut.ParseArguments<FakeOptionsWithNullDefault>(new string[0]);
+
+            // Verify outcome
+            Assert.Null(result.Value.IntSequence);
+            // Teardown
+        }
     }
 }

src/CommandLine/Core/InstanceBuilder.cs

@@ -80,12 +80,12 @@ public static ParserResult<T> Build<T>(
                     sp => sp.Value.FromJust())
                 .SetProperties(specPropsWithValue,
                     sp => sp.Value.IsNothing() && sp.Specification.DefaultValue.IsJust(),
-                    sp => sp.Specification.DefaultValue.FromJust())
-                .SetProperties(specPropsWithValue,
-                    sp => sp.Value.IsNothing()
-                        && sp.Specification.ConversionType.ToDescriptor() == DescriptorType.Sequence
-                        && sp.Specification.DefaultValue.MatchNothing(),
-                    sp => sp.Property.PropertyType.GetGenericArguments().Single().CreateEmptyArray());
+                    sp => sp.Specification.DefaultValue.FromJust());
+                //.SetProperties(specPropsWithValue,
+                //    sp => sp.Value.IsNothing()
+                //        && sp.Specification.ConversionType.ToDescriptor() == DescriptorType.Sequence
+                //        && sp.Specification.DefaultValue.MatchNothing(),
+                //    sp => sp.Property.PropertyType.GetGenericArguments().Single().CreateEmptyArray());
 
             var validationErrors = specPropsWithValue.Validate(SpecificationPropertyRules.Lookup)
                 .OfType<Just<Error>>().Select(e => e.Value);

src/CommandLine/OptionAttribute.cs

@@ -153,15 +153,7 @@ public int Max
         public object DefaultValue
         {
             get { return this.defaultValue; }
-            set
-            {
-                if (value == null)
-                {
-                    throw new ArgumentNullException("value");
-                }
-
-                this.defaultValue = value;
-            }
+            set { this.defaultValue = value; }
         }
 
         /// <summary>