Allow empty strings to convert to nullable

src/Microsoft.Extensions.Configuration.Binder/ConfigurationBinder.cs

@@ -382,6 +382,10 @@ namespace Microsoft.Extensions.Configuration
         {
             if (type.GetTypeInfo().IsGenericType && type.GetGenericTypeDefinition() == typeof(Nullable<>))
             {
+                if (string.IsNullOrEmpty(value))
+                {
+                    return null;
+                }
                 return ConvertValue(Nullable.GetUnderlyingType(type), value);
             }
 

test/Microsoft.Extensions.Configuration.Binder.Test/ConfigurationBinderTests.cs

@@ -152,6 +152,21 @@ namespace Microsoft.Extensions.Configuration.Binder.Test
             Assert.Equal(null, options.Section.Value);
         }
 
+        [Fact]
+        public void EmptyStringIsNullable()
+        {
+            var dic = new Dictionary<string, string>
+            {
+                {"empty", ""},
+            };
+            var configurationBuilder = new ConfigurationBuilder();
+            configurationBuilder.AddInMemoryCollection(dic);
+            var config = configurationBuilder.Build();
+
+            Assert.Null(config.GetValue<bool?>("empty"));
+            Assert.Null(config.GetValue<int?>("empty"));
+        }
+
         [Fact]
         public void GetScalarNullable()
         {