Present error instead of throwing exception for empty argument to FileSystemInfo type (#1704)

* Error instead of exception for FileSystemInfo null paths

* Revert autoformat

Author: therealchjones

src/System.CommandLine.Tests/Binding/TypeConversionTests.cs

@@ -65,6 +65,21 @@ public void Command_argument_of_FileInfo_returns_null_when_argument_is_not_provi
                   .BeNull();
         }
 
+        [Fact]
+        public void Argument_of_FileInfo_that_is_empty_results_in_an_informative_error()
+        {
+            var option = new Option<FileInfo>("--file");
+            var result = option.Parse(new string[] { "--file", "" });
+
+            result.Errors
+                  .Should()
+                  .ContainSingle()
+                  .Which
+                  .Message
+                  .Should()
+                  .Contain("Cannot parse argument '' for option '--file'");
+        }
+
         [Fact]
         public void Argument_of_array_of_FileInfo_can_be_called_without_custom_conversion_logic()
         {

src/System.CommandLine/Binding/ArgumentConverter.StringConverters.cs

@@ -62,6 +62,11 @@ internal static partial class ArgumentConverter
 
         [typeof(DirectoryInfo)] = (string path, out object? value) =>
         {
+            if (String.IsNullOrEmpty(path))
+            {
+                value = default;
+                return false;
+            }
             value = new DirectoryInfo(path);
             return true;
         },
@@ -80,12 +85,22 @@ internal static partial class ArgumentConverter
 
         [typeof(FileInfo)] = (string path, out object? value) =>
         {
+            if (String.IsNullOrEmpty(path))
+            {
+                value = default;
+                return false;
+            }
             value = new FileInfo(path);
             return true;
         },
 
         [typeof(FileSystemInfo)] = (string path, out object? value) =>
         {
+            if (String.IsNullOrEmpty(path))
+            {
+                value = default;
+                return false;
+            }
             if (Directory.Exists(path))
             {
                 value = new DirectoryInfo(path);